OSX Only Problems

I'm working with my lead artist, who lives about 2000 miles away, and he reports to me that on his OSX machine, the engine does all sorts of very bad things that I've never seen before, on OSX 1.4, Linux, and Windows builds of TGE1.5. He says (and has sent screen shots) of objects that get rendered only halfway and/or with big sections removed, and that the game has some kind of memory or cycle leak, such that it will lock up in about 5 minutes of play. The strangest part of these reports is that it is only happening about 50% of the time!

I've poured through the console logs, looking for any hint- and there's nothing. We have nearly identical Macbook Pros (his slightly newer)- only substancial difference is he's on 10.5 and I'm on 10.4, and I'm building the game on 10.4. None of these problems have appeared on any other platform, and I build on all three daily. There has been NO sign of this on my Tiger mac. He's going to build the game on 10.5 tomorrow, we'll see if that makes any difference (it would sure make me have to bite the bullet and upgrade), but my gut tells me that's a 50-50 shot at best. Anybody else experienced anything like this?