bbPress.org

That’s really interesting and definitely would be really annoying.

There’s never been an official mechanism to change slugs in bbPress but it should not touch them during upgrades.

I have to assume there was a bug in 0.8.3 where it would create bad or invalid slugs and that was some kind of attempt to fix the issue in the newer 0.9 code.

Be sure to note this in TRAC, otherwise it might not be seen by the developers.