[xmonad] On mac os the window boundaries are sometimes drawn, sometimes not, and sometimes partially.

I haven't figured out exactly when each situation occurs... but one thing is for certain, if I'm doing full screen X11.app and switch to a different app then come back, the borders don't get redrawn. I can press mod+space to get them to refresh manually, but they're not always drawn correctly even then. Sometimes there will be partial-borders drawn around part of a window. Any hints on where to start looking to figure out this problem? -Ryan