I was just remembering that there was a kind of similar sounding bug with Wacom back quite a while ago:
http://moi3d.com/forum/index.php?webtag=MOI&msg=8731.101

There is a standalone test case app attached there that reproduced the bug outside of MoI, which I sent to Wacom and they fixed it in their updated drivers.

I wonder if there's a bug in some example tablet driver code from Apple.

- Michael