Well that didn't help...
Downgraded to 5.1.12
i assume you did 5.2.12... but yah, i have threads 7.2.2 and 7.5.4.2 running on same box with no problem... (apache 2.2.14, mysql 5.1.41, php 5.2.12)
sooooo... looks like you'll need someone to take a closer looksee

good luck to you..