[Elias]

Arrgh! Horrors!

The problem is caused by the bb_append_meta invocation in line 2075 of functions.php. The query destroys the last SQL_CALC_FOUND_ROWS and so the count is wrong. A quick and dirty workaround is to change 'append_meta' => false to 'append_meta' => false in the $defaults array in line 2021 of functions.php. But this only works if the append_meta argument is not given in the bb_user_search call.

Now the problem is more complicated as I suspected earlier. It is a problem for the hackers that make bbPress. No further searching for bugs from me, the problem should be clear. (It is clear enough to me after reading lots of code from other people.) I expect it to be fixed in the next release.