So far Premier is the only program to do this, and the only major addition or change to my system was the OSX (lion) upgrade. My iMac is the 21.5" display and I have to drag back from the right (offscreen) any new window upon opening.
I would appreciate hearing of any solutions to this problem.
Im not a Mac person and dont really know if this will fix it but try re-setting the work area and see if it then sticks.
Show screen shots if you can.
Maybe another Mac user can help.