If it is APE ...
... then I wouldn't fully blame Apple on this one. I do remember some similar shoddy extensions crapping out after some System 7 updates back in '94 me thinks. Apps that do low-level kernel interaction should check versions before running, though the OS should do them too ;)
That said, I think the worst OS bug I've *ever* seen (bar Vista) might be the "disk 1" we got in some 7.5.x update. For those who don't know:
Back then, floppy disk installations were still common, and with multi-disk installs you usually inserted disk 1, run the installer, and for disks 2 and beyond you would insert disk 2, or insert disk 1, then insert disk X and go on. Except on this particular update, something weird happened, and now after disk 2 you would enter the "endless cycle of doom" where you insert disk 2, OS reads a sector, pukes disk 2, ask disk 1, read sector, puke it, ask disk 2 ... you get the idea.
After 200 cycles of "disk 1,2,1,2,1,2,1,2,1,2,1,3,1,3,1,3,1,3" my dad just went "aaah fuck it!" and returned to the older OS version. Now that was bad, real bad. Of course, Apple issued a fix pretty quick, but these were the days before broadband Internet, or even used for such updates: that fix would be sent by mail, which in our case took weeks.
Still, much quicker than the major fixing overhaul required by Vista...
Oh and by the way, I hate what Jobs has done to my formerly beloved Apple, but at least they are still kicking MS ass.