HTC had disabled it for a bit because they thought it might be causing lag. Dunno if they still turn it off/on to keep testing that theory.
I do know that at one point, there was a rebuild done (when everyone's total posts went down about 30%) that resulted in a blind spot to the BBS search function... about a year's worth of it.
You can tell that period because the user name for the original poster is usually blacked out, even if they have a current account.