I do not believe this is a bug, but rather it is status-bydesign.
As the edit notification system is currently designed, users are not notified when a minor edit is made to one of their own posts. The exact criteria are:
a non-trivial edit is one which changes at least 10 characters (this is using a diff algorithm, so it's not a simple add/delete; and is naturally a little fuzzy). For the "technical" sites (where code highlighting is enabled) changes to code of at least 2 characters are considered non-trivial.
According to this, changes to tags are considered trivial and will not generate a notification.