I'm having this problem too it's really annoying. It effectively renders my 2nd non-retina screen useless for Photoshop at the moment.
Any solutions are welcome... I'd like to keep the GPU enhancements running if possible.
I asked the Apple Care Support several months ago, they told me, that it looks like a Adobe-bug.
i also have no other solution than disable the GPU enhancements...
sometimes closing the Safari-Browser helps...
And has AppleCare ever admitted to something being an Apple bug, even when Apple has already admitted to the bug and commited to a fix?
And I'll bet this problem only happens on 10.8 (which has several known GPU driver issues).
I am running the latest up-to-date version of Photoshop.
Curiously, for some windows it displays fine on the second screen, whereas on others it goes absolutely nuts like the OP's attached image!
I'm also getting alot of persistent graphics that shouldn't be there (on my primary retina monitor), things like artifacts from the free-transform overlay and existing documents (when tabbing between open psds). I could go into more detail, but I'm starting to think it's a separate issue and warrants it's own post, which I'll try to do shortly.
Not to throw more complexity in here, but have any of you with this problem tried the three different Advanced Drawing Modes for graphics processor operation?
Photoshop - Preferences - Performance, then press the [Advanced Settings...] button.
Make sure to fully Quit Photoshop and restart it after making any changes here, before testing.