Settings aren't saved

[fwosar]

It appears no settings are saved. Even changing them directly within the settings table makes no difference. The settings are completely ignored.

Environment:
  Redmine version                3.4.1.stable
  Ruby version                   2.3.1-p112 (2016-04-26) [x86_64-linux-gnu]
  Rails version                  4.2.8
  Environment                    production
  Database adapter               Mysql2
SCM:
  Subversion                     1.9.3
  Git                            2.7.4
  Filesystem                     
Redmine plugins:
  redmine_agile                  1.4.4
  redmine_ckeditor               1.1.4
  redmine_default_assign         0.6
  redmine_slack                  0.2
  redmine_theme_changer          0.3.0
  redmine_wiki_extensions        0.8.0