affacat, I won't be fixing this one because I've written a new alternative to both this plugin and private forums. It allows hidden forums with entry by either user number or user type. It uses newer abilities from bbPress 0.9 to pre-filter all results instead of what these plugins mostly do with filtering the results afterwards. It should also be faster.
The catch is it's brand new so I'm still awaiting bug reports and doesn't have an admin menu yet:
http://bbpress.org/plugins/topic/hidden-forums/