Update, this also happends when creating a group. The group is created though.
Forum posts doesn’t work either, getting the same flashing 404 page, bbpress installed.
Played around a bit with it, but still have the problems. Everything seems to work pretty good though, but I get a 404 error when clicking e.g. create group… I then get redirected to the correct page, when I click create group button after filling out the form I get the same 404 error, and then get redirected to the newly created group page.
that helped.
