diff --git a/app/controllers/projects_controller.rb b/app/controllers/projects_controller.rb
index 2a42c99ed..f7065e130 100644
--- a/app/controllers/projects_controller.rb
+++ b/app/controllers/projects_controller.rb
@@ -96,14 +96,14 @@ class ProjectsController < ApplicationController
 
   def new
     @issue_custom_fields = IssueCustomField.sorted.to_a
-    @trackers = Tracker.sorted.to_a
+    @trackers = Tracker.active.sorted.to_a
     @project = Project.new
     @project.safe_attributes = params[:project]
   end
 
   def create
     @issue_custom_fields = IssueCustomField.sorted.to_a
-    @trackers = Tracker.sorted.to_a
+    @trackers = Tracker.active.sorted.to_a
     @project = Project.new
     @project.safe_attributes = params[:project]
 
@@ -140,7 +140,7 @@ class ProjectsController < ApplicationController
 
   def copy
     @issue_custom_fields = IssueCustomField.sorted.to_a
-    @trackers = Tracker.sorted.to_a
+    @trackers = Tracker.active.sorted.to_a
     @source_project = Project.find(params[:id])
     if request.get?
       @project = Project.copy_from(@source_project)
@@ -201,7 +201,10 @@ class ProjectsController < ApplicationController
     @issue_custom_fields = IssueCustomField.sorted.to_a
     @issue_category ||= IssueCategory.new
     @member ||= @project.members.new
-    @trackers = Tracker.sorted.to_a
+    # Show active trackers plus any inactive trackers already assigned to this project
+    @trackers = Tracker.sorted.where(:active => true).or(
+      Tracker.sorted.where(:id => @project.tracker_ids)
+    ).sorted.to_a
 
     @version_status = params[:version_status] || 'open'
     @version_name = params[:version_name]
diff --git a/app/controllers/trackers_controller.rb b/app/controllers/trackers_controller.rb
index 4080df618..308b48b4a 100644
--- a/app/controllers/trackers_controller.rb
+++ b/app/controllers/trackers_controller.rb
@@ -86,6 +86,18 @@ class TrackersController < ApplicationController
     end
   end
 
+  def lock
+    @tracker = Tracker.find(params[:id])
+    @tracker.update!(:active => false)
+    redirect_to trackers_path
+  end
+
+  def unlock
+    @tracker = Tracker.find(params[:id])
+    @tracker.update!(:active => true)
+    redirect_to trackers_path
+  end
+
   def destroy
     @tracker = Tracker.find(params[:id])
     if @tracker.issues.empty?
diff --git a/app/models/issue.rb b/app/models/issue.rb
index 4c16fb6af..7e7d0d1d1 100644
--- a/app/models/issue.rb
+++ b/app/models/issue.rb
@@ -1695,7 +1695,13 @@ class Issue < ApplicationRecord
   # Returns a scope of trackers that user can assign project issues to
   def self.allowed_target_trackers(project, user=User.current, current_tracker=nil)
     if project
-      scope = project.trackers.sorted
+      scope = project.trackers.sorted.active
+      # Always include the current tracker even if it is inactive
+      if current_tracker
+        scope = Tracker.sorted.where(
+          :id => scope.pluck(:id) | [current_tracker]
+        )
+      end
       unless user.admin?
         roles = user.roles_for_project(project).select {|r| r.has_permission?(:add_issues)}
         unless roles.any? {|r| r.permissions_all_trackers?(:add_issues)}
@@ -1810,7 +1816,9 @@ class Issue < ApplicationRecord
         copy.author = author
         copy.project = project
         copy.parent_issue_id = copied_issue_ids[child.parent_id]
-        unless child.fixed_version.present? && child.fixed_version.status == 'open'
+        if fixed_version_id != @copied_from.fixed_version_id
+          copy.fixed_version_id = fixed_version_id
+        elsif !(child.fixed_version.present? && child.fixed_version.status == 'open')
           copy.fixed_version_id = nil
         end
         unless child.assigned_to_id.present? &&
diff --git a/app/models/project.rb b/app/models/project.rb
index d15c29882..55c66169d 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -139,9 +139,9 @@ class Project < ApplicationRecord
     if !initialized.key?('trackers') && !initialized.key?('tracker_ids')
       default = Setting.default_projects_tracker_ids
       if default.is_a?(Array)
-        self.trackers = Tracker.where(:id => default.map(&:to_i)).sorted.to_a
+        self.trackers = Tracker.where(:id => default.map(&:to_i)).active.sorted.to_a
       else
-        self.trackers = Tracker.sorted.to_a
+        self.trackers = Tracker.active.sorted.to_a
       end
     end
     # rubocop:enable Style/NegatedIf
diff --git a/app/models/tracker.rb b/app/models/tracker.rb
index e33ec333c..4ec260fc6 100644
--- a/app/models/tracker.rb
+++ b/app/models/tracker.rb
@@ -46,6 +46,7 @@ class Tracker < ApplicationRecord
 
   scope :sorted, lambda {order(:position)}
   scope :named, lambda {|arg| where("LOWER(#{table_name}.name) = LOWER(?)", arg.to_s.strip)}
+  scope :active, lambda {where(:active => true)}
 
   # Returns the trackers that are visible by the user.
   #
@@ -75,6 +76,7 @@ class Tracker < ApplicationRecord
     'default_status_id',
     'is_in_roadmap',
     'private_by_default',
+    'active',
     'core_fields',
     'position',
     'custom_field_ids',
diff --git a/app/views/trackers/index.html.erb b/app/views/trackers/index.html.erb
index 12dc0aa4c..074f3f231 100644
--- a/app/views/trackers/index.html.erb
+++ b/app/views/trackers/index.html.erb
@@ -11,11 +11,11 @@
   <th><%=l(:field_default_status)%></th>
   <th><%=l(:field_description)%></th>
   <th></th>
-  <th></th>
+  <th class="tracker-buttons-col"></th>
   </tr></thead>
   <tbody>
 <% for tracker in @trackers %>
-  <tr>
+  <tr class="<%= tracker.active? ? '' : 'tracker-locked' %>">
   <td class="name"><%= link_to tracker.name, edit_tracker_path(tracker) %></td>
   <td><%= tracker.default_status.name %></td>
   <td class="description"><%= tracker.description %></td>
@@ -26,9 +26,14 @@
       </span>
     <% end %>
   </td>
-  <td class="buttons">
+  <td class="buttons tracker-buttons-col">
     <%= reorder_handle(tracker) %>
     <%= link_to sprite_icon('copy', l(:button_copy)), new_tracker_path(:copy => tracker), :class => 'icon icon-copy' %>
+    <% if tracker.active? %>
+      <%= link_to sprite_icon('lock', l(:button_lock)), lock_tracker_path(tracker), :method => :put, :class => 'icon icon-lock' %>
+    <% else %>
+      <%= link_to sprite_icon('unlock', l(:button_unlock)), unlock_tracker_path(tracker), :method => :put, :class => 'icon icon-unlock' %>
+    <% end %>
     <%= delete_link tracker_path(tracker) %>
   </td>
   </tr>
@@ -36,6 +41,14 @@
   </tbody>
 </table>
 
+<style>
+  tr.tracker-locked td { opacity: 0.6; }
+  table.trackers th.tracker-buttons-col,
+  table.trackers td.tracker-buttons-col { width: 1%; white-space: nowrap; }
+  table.trackers td.tracker-buttons-col a.icon-lock,
+  table.trackers td.tracker-buttons-col a.icon-unlock { display: inline-block; min-width: 82px; }
+</style>
+
 <% html_title(l(:label_tracker_plural)) -%>
 
 <%= javascript_tag do %>
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 2a30a9d3a..e48d40319 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -672,6 +672,7 @@ en:
   label_tracker_plural: Trackers
   label_tracker_all: All trackers
   label_tracker_new: New tracker
+  label_tracker_locked: Locked
   label_workflow: Workflow
   label_issue_status: Issue status
   label_issue_status_plural: Issue statuses
diff --git a/config/locales/ja.yml b/config/locales/ja.yml
index 05b9ab47d..a23f96d6c 100644
--- a/config/locales/ja.yml
+++ b/config/locales/ja.yml
@@ -1201,6 +1201,7 @@ ja:
   label_no_preview: このファイルはプレビューできません
   error_no_tracker_allowed_for_new_issue_in_project: このプロジェクトにはチケットの追加が許可されているトラッカーがありません
   label_tracker_all: すべてのトラッカー
+  label_tracker_locked: ロック済み
   label_new_project_issue_tab_enabled: '"新しいチケット" タブを表示'
   setting_new_item_menu_tab: 新規オブジェクト作成タブ
   label_new_object_tab_enabled: '"+" ドロップダウンを表示'
diff --git a/config/routes.rb b/config/routes.rb
index 9edb2f855..7efa22646 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -350,6 +350,10 @@ Rails.application.routes.draw do
   delete 'groups/:id/users/:user_id', :to => 'groups#remove_user', :id => /\d+/, :as => 'group_user'
 
   resources :trackers, :except => :show do
+    member do
+      put 'lock'
+      put 'unlock'
+    end
     collection do
       match 'fields', :via => [:get, :post]
     end
diff --git a/db/migrate/20260612000000_add_active_to_trackers.rb b/db/migrate/20260612000000_add_active_to_trackers.rb
new file mode 100644
index 000000000..c34404572
--- /dev/null
+++ b/db/migrate/20260612000000_add_active_to_trackers.rb
@@ -0,0 +1,5 @@
+class AddActiveToTrackers < ActiveRecord::Migration[8.1]
+  def change
+    add_column :trackers, :active, :boolean, :default => true, :null => false
+  end
+end
diff --git a/test/fixtures/trackers.yml b/test/fixtures/trackers.yml
index d5022da6b..312e66022 100644
--- a/test/fixtures/trackers.yml
+++ b/test/fixtures/trackers.yml
@@ -4,15 +4,18 @@ trackers_001:
   id: 1
   default_status_id: 1
   position: 1
+  active: true
   description: Description for Bug tracker
 trackers_002:
   name: Feature request
   id: 2
   default_status_id: 1
   position: 2
+  active: true
   description: Description for Feature request tracker
 trackers_003:
   name: Support request
   id: 3
   default_status_id: 1
   position: 3
+  active: true
diff --git a/test/functional/trackers_controller_test.rb b/test/functional/trackers_controller_test.rb
index e55d8ffc8..879c572aa 100644
--- a/test/functional/trackers_controller_test.rb
+++ b/test/functional/trackers_controller_test.rb
@@ -304,6 +304,41 @@ class TrackersControllerTest < Redmine::ControllerTest
     end
   end
 
+  def test_lock
+    tracker = Tracker.find(1)
+    assert tracker.active?
+    put :lock, :params => {:id => 1}
+    assert_redirected_to :action => 'index'
+    assert_not tracker.reload.active?
+  end
+
+  def test_unlock
+    tracker = Tracker.find(1)
+    tracker.update!(active: false)
+    put :unlock, :params => {:id => 1}
+    assert_redirected_to :action => 'index'
+    assert tracker.reload.active?
+  end
+
+  def test_lock_requires_admin
+    @request.session[:user_id] = 2
+    put :lock, :params => {:id => 1}
+    assert_response :forbidden
+  end
+
+  def test_index_shows_lock_button_for_active_tracker
+    get :index
+    assert_response :success
+    assert_select 'a[href=?]', lock_tracker_path(1)
+  end
+
+  def test_index_shows_unlock_button_for_locked_tracker
+    Tracker.find(1).update!(active: false)
+    get :index
+    assert_response :success
+    assert_select 'a[href=?]', unlock_tracker_path(1)
+  end
+
   def test_post_fields
     post :fields, :params => {
       :trackers => {
diff --git a/test/unit/issue_test.rb b/test/unit/issue_test.rb
index a5c0bbb87..3ed2f7fd9 100644
--- a/test/unit/issue_test.rb
+++ b/test/unit/issue_test.rb
@@ -1539,6 +1539,22 @@ class IssueTest < ActiveSupport::TestCase
     assert_equal [3, nil], copy.children.map(&:fixed_version_id)
   end
 
+  def test_copy_should_propagate_version_change_to_subtasks
+    parent = Issue.generate!(:fixed_version_id => 3)
+    child1 = Issue.generate!(:parent_issue_id => parent.id, :subject => 'Child 1', :fixed_version_id => 3)
+    child2 = Issue.generate!(:parent_issue_id => parent.id, :subject => 'Child 2', :fixed_version_id => nil)
+
+    new_version = Version.generate!(:project => Project.find(1))
+    copy = parent.reload.copy(:fixed_version_id => new_version.id)
+
+    assert_difference 'Issue.count', 3 do
+      assert copy.save
+    end
+
+    assert_equal new_version.id, copy.fixed_version_id
+    assert_equal [new_version.id, new_version.id], copy.children.map(&:fixed_version_id)
+  end
+
   def test_copy_should_clear_subtasks_assignee_if_is_locked
     user = User.find(2)
 
@@ -1909,6 +1925,23 @@ class IssueTest < ActiveSupport::TestCase
     assert_equal [], issue.allowed_target_trackers(User.find(2)).ids
   end
 
+  def test_allowed_target_trackers_excludes_locked_trackers
+    Tracker.find(1).update!(active: false)
+    issue = Issue.new(:project => Project.find(1))
+    ids = Issue.allowed_target_trackers(Project.find(1), User.find(1)).ids
+    assert_not_includes ids, 1
+    assert_includes ids, 2
+    assert_includes ids, 3
+  end
+
+  def test_allowed_target_trackers_includes_current_tracker_even_if_locked
+    tracker = Tracker.find(1)
+    tracker.update!(active: false)
+    issue = Issue.generate!(:project => Project.find(1), :tracker => tracker)
+    ids = issue.allowed_target_trackers(User.find(1)).ids
+    assert_includes ids, 1
+  end
+
   def test_allowed_target_trackers_should_include_current_tracker
     user = User.generate!
     role = Role.generate!
diff --git a/test/unit/tracker_test.rb b/test/unit/tracker_test.rb
index a9728b9b2..5f65f48be 100644
--- a/test/unit/tracker_test.rb
+++ b/test/unit/tracker_test.rb
@@ -167,4 +167,31 @@ class TrackerTest < ActiveSupport::TestCase
     assert tracker.respond_to?(:description)
     assert_equal tracker.description, "Description for Bug tracker"
   end
+
+  def test_active_scope_returns_only_active_trackers
+    Tracker.find(1).update!(active: false)
+    active_ids = Tracker.active.pluck(:id)
+    assert_not_includes active_ids, 1
+    assert_includes active_ids, 2
+    assert_includes active_ids, 3
+  end
+
+  def test_tracker_is_active_by_default
+    tracker = Tracker.new(:name => 'New tracker', :default_status_id => 1)
+    assert tracker.active?
+  end
+
+  def test_lock_tracker
+    tracker = Tracker.find(1)
+    assert tracker.active?
+    tracker.update!(active: false)
+    assert_not tracker.reload.active?
+  end
+
+  def test_unlock_tracker
+    tracker = Tracker.find(1)
+    tracker.update!(active: false)
+    tracker.update!(active: true)
+    assert tracker.reload.active?
+  end
 end