I had previously thought that using mixed bit depths was working in rootless mode, but I have since found one problem.
One monitor is set to 24 bits and the other is set to 15. Windows in the 15bit screen don't always update when the contents change. I think this explains the previous bug I reported with xteddy.
What video hardware is driving the 15-bit monitor? Is the 15-bit monitor the primary XDarwin screen? Can you set the 15-bit screen to 24-bit? If you can, are the updates still wrong?
The 15bit monitor is secondary and unaccelerated. It's just a Mach64 card. I can't set it to Millions mode due to limited video memory and the resolution I want to use.
IIRC setting both to millions did solve the problem previously.