Redmine

When trying to enter minutes into the Estimated Time field in a ticket, the time gets rounded down or up to full hours after I click the save button. It doesn't matter whether I enter in decimal format (0.25) or in hours format (00:15). I also can't find any settings where to change that, neither can't I remember having changed any configuration in Redmine. Are there any settings related to this?

Environment

 Redmine version                2.5.1.stable
  Ruby version                   2.1.2-p95 (2014-05-08) [x86_64-linux]
  Rails version                  3.2.17
  Environment                    production
  Database adapter               PostgreSQL

Plugins

  line_numbers                   1.0.0
  redmine_agile                  1.3.12
  redmine_all_files              0.0.3
  redmine_bootstrap_kit          0.1
  redmine_didyoumean             1.2.0
  redmine_github_hook            2.2.0
  redmine_gitlab_hook            0.0.1
  redmine_inline_note_images_plugin 0.0.1
  redmine_jstoolbar_ext          0.2.1
  redmine_jstoolbar_ext_coderay  0.2.0
  redmine_jstoolbar_ext_images   0.2.0
  redmine_login_audit            0.1.4
  redmine_mailstatus             0.0.1
  redmine_pipeline_plugin        1.0.0
  redmine_rubycas                0.0.6
  redmine_time_tracker           0.9.15

We have used these plugins for quite long without any issues, I just upgraded them a couple of weeks ago. Unfortunately I cannot tell (if) which plugins might be the cause.