Window does not resize on 3rd monitor
 

I have a client that has added a 3rd monitor to his studio setup. He is running PT 10 on a Mac Pro ("cheese grater" version) and has an odd issue where windows on one of his new monitors will not resize properly. The new "3rd" monitor is a 1080P TV and when any window in PT is dragged onto it, it seems to loose the ability to be expanded. The windows can be shrunk, but not enlarged. So we found that we have to drag the window back to another monitor, enlarge it, then drag it back. This only happens with PT, other applications (mail, safari, etc.) operate just fine with the ability to shrink or expand having normal results. Also the + button (to maximize) doesn't work either. Has anyone else experienced a similar issue? Has anyone found a solution? I asked if he would be willing to upgrade to a newer version of PT but he would also have to upgrade his OS most likely, some other software, and renew some plugin subscriptions, so he would rather avoid that for the time being. Thanks!