Why doesn't this work in windowed mode?

Hmm interesting. Well, the second thing you said Skid is of high interest to me - if I can try selecting the backbuffer and then check the error messages and find it's not allowed/available, that in itself can act as confirmation that there is no backbuffer, which is basically what I'm after. Thanks!

And yah, looks like either an apple bug or just some wierd way that they've got things set up on that older system. Having said that I get the same problem on my much newer iMac.

I'll go with the error message method and dump this graphical test, it's wasting too much time for me.

Thanks.