Index: issue.rb
===================================================================
--- issue.rb	(revision 16557)
+++ issue.rb	(working copy)
@@ -241,6 +241,7 @@
   def reload(*args)
     @workflow_rule_by_attribute = nil
     @assignable_versions = nil
+    @assignable_users = nil
     @relations = nil
     @spent_hours = nil
     @total_spent_hours = nil
@@ -911,12 +912,15 @@
 
   # Users the issue can be assigned to
   def assignable_users
-    users = project.assignable_users(tracker).to_a
-    users << author if author && author.active?
-    if assigned_to_id_was.present? && assignee = Principal.find_by_id(assigned_to_id_was)
-      users << assignee
+    return @assignable_users unless @assignable_users.nil?
+    user_ids = []
+    user_ids << author_id if author && author.active?
+    user_ids << assigned_to_id_was if assigned_to_id_was.present?
+    if project
+      project_users = project.assignable_users(tracker)
+      user_ids.concat project_users.reorder(nil).pluck(:id)
     end
-    users.uniq.sort
+    @assignable_users = user_ids.empty? ? [] : Principal.where(:id => user_ids).sorted.to_a
   end
 
   # Versions that the issue can be assigned to