There seems to have been a glitch of some sort regarding group settings. This resets the rights given to a specific role in your group to the maximum allowed rights (ie, Full Control over gallery, journals, any deviant can join as this role without a vote, etc).
The problem here is that if it affects the Founder or Co-Founder roles, ANY deviant can join your group as a Founder or Co-Founder without a vote, and they'll have the authority to kick out and or block the original staff!
I had hoped it was just a fluke within our own group, but after checking around, I found that I could become a Founder on numerous groups!
Check your settings under Admin Area -> Manage Members!