When
PS is doing things wierd, it's usually because the preference file has got corrupted, its almost always worth clearing it out.
To clear it, close
PS, then on re-launch press Ctrl+Shift+Alt
PS will ask if you if its OK to delete your preference file, click OK.
PS creates a new preference file automatically.
The thing is you'll have lost all your preferences. Because of this, its always worth keeping a good copy of your preference file, Then once your file has been cleared, and the problem resolved, you can re-instate your preferences.