MyBB Community Forums

I added a subforum today, and set the access permission as I wanted (only a few usergroups were able to access it), but after creating the subforum, the permissions got reset, and everybody could access the forum... I edited it, readded the custom permissions, submitted, and then it got reset again.

Is this a known bug or is it just on my forum?

try to re-build your forum permission cache that should fix it..