Redmine

When editing the issue, fields are displayed for modification in "Change properties" area.
In the area, "Start date" and "Due date" have string-fields and there are Icons for Datepicker right of the string-fields normally.

But, if an issue has a child issue ( or issues ), Icons for Datepicker right of the string-fields does NOT appear when editing the issue.
If I remove the child from the parent and enter edit screen, Icons for Datepicker come back again. Wow.

This phenomenon happens 100% of probability.
We made sure that it does happen with Firefox and Internet Explorer through the testing.

Attached is the ZIP of screen captures of this phenomenon. File names represent what was happening in the screen. Hope this helps.

Redmine configuration (from "Information" of "Redmine") are as follows.
The phenomenon happens on both configurations.

• production system: Linux based
  

  Environment:
    Redmine version                3.1.1.stable
    Ruby version                   2.2.3-p173 (2015-08-18) [x86_64-linux]
    Rails version                  4.2.4
    Environment                    production
    Database adapter               PostgreSQL
  SCM:
    Git                            1.7.1
    Filesystem                     
  Redmine plugins:
    redmine_absolute_dates         0.0.3
    redmine_dmsf                   1.5.6
    redmine_document_view_overwrite 0.0.1
    redmine_enter_cancel           0.0.2
    redmine_good_job               0.0.1.1
    redmine_issue_templates        0.1.0
    redmine_local_avatars          0.1.1
    redmine_pivot_table            0.0.4
    redmine_show_issue_assignee_avatar 0.0.1
    redmine_vividtone_my_page_blocks 20150614
    redmine_wiki_lists             0.0.6
    sidebar_hide                   0.0.7
  

• Testing system: Windows 7 based
  

  Environment:
    Redmine version                3.1.1.stable
    Ruby version                   2.0.0-p645 (2015-04-13) [i386-mingw32]
    Rails version                  4.2.4
    Environment                    production
    Database adapter               Mysql2
  SCM:
    Subversion                     1.8.11
    Git                            1.9.5
    Filesystem                     
  Redmine plugins:
    redmine_good_job               0.0.1.1
    redmine_issues_summary_graph   0.0.9
    redmine_local_avatars          1.0.3
    redmine_pivot_table            0.0.4
    redmine_show_issue_assignee_avatar 0.0.1
    redmine_vividtone_my_page_blocks 20150614
    redmine_wiki_lists             0.0.6