This requires access to the DB and to codebase:
A) Upgrade from Moodle 2.1 to master (integration.git).
1) Go to admin->plugins->filters.
2) Verify you can see there the glossary and data filters.
3) Verify that the filter_active table contains record(s) for filter/glossary and filter/data (but not for mod/glossary and mod/data).
4) Verify that mod/glossary/filter.php and mod/data/filter.php do not exist.
5) Create mod/forum/filter.php (any content).
6) Verify that one new row is shown in admin->plugins->filters (in red, unnamed but related with mod/forum).
7) Verify that one new record in the filter_active table for the just created mod/forum filter.
8) Delete the file mod/forum/filter.php and the record in filter_active for mod/forum.
9) Verify that admin->plugins->filters is back to normal (no mod/forum shown anymore).
10) Create mod/data/filter.php and mod/data/glossary.php (any content).
11) Verify that the 2 new created filters are not shown in admin->plugins->filters.
12) Verify that there are no records in filter_active corresponding to mod/data and mod/glossary (but the filter/data and filter/glossary ones remains).
13) Delete the mod/data/filter.php and mod/data/glossary.php files.
B) Repeat steps 1-13 into a installed master (2.2) site.