Low letter tags bug

After enabling "force lower-case tags" in admin settings and running python manage.py fix_question_tags I get get tags suggested which never existed before like

_internal_Admin_1
_internal_SecondUser_2
_internal_ThirdUser_3
...

The structure of the strings is:

_internal_ + SomeUserName + User serial number

A see these tags only as suggested tags not in the tag list or cloud