Redmine

This function was already implemented. I'm using redmine 2.2.1 and there a popup appears after typing two or more letters.

Which Redmine version do you use and which browser do you use?

Using Mozilla Firefox and version 2.2.3

This works in my Redmine 2.3.1. When I type at least two letters in parent task field, a dropdown list appears. My configuration is:

Environment:
  Redmine version                          2.3.1.stable
  Ruby version                             1.9.3 (i386-mingw32)
  Rails version                            3.2.13
  Environment                              production
  Database adapter                         Mysql2
Redmine plugins:
  clipboard_image_paste                    1.5
  projects_tree_view                       0.0.8
  redmine_apijs                            4.2.0
  redmine_code_review                      0.6.2
  redmine_didyoumean                       1.2.0
  redmine_favourite_projects               0.6
  redmine_information                      1.0.2
  redmine_issue_checklist                  2.0.5
  redmine_local_avatars                    0.1.1
  redmine_pastebin                         0.2.0
  redmine_plugin_views_revisions           0.0.1
  redmine_theme_changer                    0.1.0
  redmine_user_issues                      0.0.2
  redmine_wiki_gchart_formula              0.0.5
  redmine_xls_export                       0.2.1
  redmine_youtube                          0.0.1
  sidebar_hide                             0.0.2
  wiking                                   0.0.3

Yea sorry for late reply but yes I was using an outdated version, seems like, I updated. Thanks