Sometimes good software just goes bad. If that ever happens to your beloved Photoshop, and you begin to experience weirdness in various forms, it may be time to rebuild its preferences.
Though, instead of rooting around your hard drive to zap this file on your own you can make Photoshop do it all by itself. The trick is to hold the Command, Option, and Shift keys (PC: Control-Alt-Shift) when you first launch the program.
For when you do, you'll be greeted witha dialog box asking if you want to delete the Photoshop settings file. Click yes, and it will dutifully build a new, fresh set of preferences just for you.