This is a bug that has been plaguing MacBooks (that have integrated Intel graphics) since the 10.5.5 update and EL 1.7. I have looked into the problem a bit, and I don't think there is much we can do. It seems to be entirely related to an update in the graphics drivers that occurred at 10.5.5.
Florian and Fedora, care to weigh in on this?
Just wondering if there are any news on that one? It's bugging me too... But fortunately I still have an iBook for mixing