Hi Rob,
This isn't reproducible on my machines, and in fact I've never seen anything so severe on Mac OS X.
These problems happen from time to time on all platforms. They can originate in graphical libraries (Qt for example) as well as in the operating system or underlying desktop manager, and can also be due to hardware errors.
As long as this is not reproducible on several machines in a consistent way, let's say that this problem belongs to the "weird things that happen" category.