Hm. So all was going well, but out of the blue our subforum searches stopped working. If i don't specify a subforum, the searches work. If I do, I get an assertion failure in sphinxapi.php @ line 290 (with 0.9.7-rc2).
I ran into the problem on -rc1, and decided to upgrade to see if it had been fixed, but it has not. I'm a tad stumped.
Edit: I seem to have fixed it by adding a "$value = intval($value);" before the assert() in sphinxapi.php. Guess this is related to the assertion failures earlier, so much for not having to cast variables