If you have a different machine you can test on that would be great to narrow it down a little. FWIW I'm testing on 10.4 here with an ATI chip, and it works perfectly, so I'm guessing either something has changed in 10.5[0], or there's a driver issue that we might (hopefully) be able to work around.

[0] It's worth noting that the LDFLAGS hack isn't necessary in 10.4, so they definitely broke something there...