To answer your last question, the Messenger Plus! forum runs on an old version of MyBB, which is not quite as fast as the current version. There are over 50,000 users on that forum.
All the bugs in the Archived - PR2 forum have been fixed in the development code for the next release. Some of the oldest bugs may have been fixed in the 686 public release, but the newer ones in the forum aren't patched in the MyBB download page.