Environment:
  Redmine version                2.5.1.stable
  Ruby version                   2.1.5-p273 (2014-11-13) [i386-linux]
  Rails version                  3.2.17
  Environment                    production
  Database adapter               Mysql2
Redmine plugins:
  buildversion_manager           0.0.1
  enervision_customization       0.1.1
  extended_gantt                 0.2.0
  issue_repo_history_merge       0.0.2
  multi_time_tracker             0.1.2
  once_assigned_ever_watcher     0.1.0
  redmine_proxy                  0.0.1
  redmine_re                     development version
  redmine_reminder               0.3.0
  redmine_wiki_lists             0.0.3
  stuff_to_do_plugin             0.4.2
  work_performance_record_to_pdf 0.0.1

The following situation:

I have a Redmine 2.5.1 instance running several plugins. One of them is called @redmine_reminder@, the other one @redmine_re@. @redmine_reminder@ was installed before @redmine_re@ and has four migration steps.
Now when I tried to migrate @redmine_re@ migration started with the fifth migration step. Unnecessary to say that it did not succeed.

In the end I managed to install both plugins by rolling back @redmine_reminder@ to version 0, fixing the broken migrations of @redmine_re@ by hand and then installing @redmine_re@ first followed by @redmine_reminder@.
For some reason the migration of @redmine_re@ started at step five because of the 0-redmine_reminder entry in @schema_migrations@. As soon as these entries were gone because of the rollback the migration of @redmine_re@ started with step 0.

So it looks like the migration for @redmine_re@ saw that there is something in schema_migrations (namely @redmine_reminder@) that is similar and therefore started with the fifth step.

I don't know if this is a job for the Redmine developers or for the Rails developers so I post it here first.