Redmine

A number of different tickets have fields that are not editable.
Affected fields are 'Priority', 'Start date', 'Due date' and 'Estimated time'.

Priority is greyed out.
The other fields show no value at all when in the edit mask wether the field is filled or not.

I am using my administrator account with full access, so I don't think it is a permission issue.

Environment:
  Redmine version                2.5.1.stable
  Ruby version                   1.9.3-p545 (2014-02-24) [x86_64-linux]
  Rails version                  3.2.17
  Environment                    production
  Database adapter               Mysql2
SCM:
  Subversion                     1.6.11
  Git                            1.7.1
  Filesystem                     
Redmine plugins:
  redmine_dashboard              2.2.2
  redmine_graphs                 0.1.0
  redmine_http_auth              0.3.0-dev-redmine-2.x
  redmine_importer               1.2.2
  redmine_information            1.0.2
  redmine_monitoring_controlling 0.1.1
  redmine_release_notes          1.3.1
  scrum2b                        2.0