What operating system and version of photoshop are you using?
Resetting the photoshop cs4 preferences might resolve the issue.
Press and hold the Shift+Ctrl+Alt keys just after starting the launch of photoshop cs4
(you have to be quick about pressing the keys or you want get the below dialog)
Keep holding the keys down until you get a dialog asking if you want to Delete the adobe photoshop settings file
I'm probably going to answer my own question, but this particular computer is WinXP (ducks from all the laughter), and CS4. I have been waiting over 5 years to upgrade everything, but there are life-reasons why it's been over 5 years, trust.
I have reset preferences a few times throughout the years, but the problem comes back. Again, I cannot narrow this down to any particular event, so maybe it's a matter of an old OS and possibly low RAM. WinXP has that 4GB cap, and it seems when my system passes 3GB of RAM, all sorts of things begin to happen, but this issue has even happened with nothing else opened.
I get this same issue, and it doesn't return until I restart photoshop.