Description of problem:

It would appear that GTK apps, most notably gimp, have issues with the offset offset when drawing using a cintiq pen when pressure sensitivity is enabled. This only happens in a configuration with Cintiq and 2nd monitor. It's doesn't happen with a single Cintiq. 

This problem can be verified by moving the cursor around: if the pen is 90 degrees from the screen, it differs where the cursor is exactly is depending where in the screen. This only happens in dual monitors with different resolutions.