Is your GPU-driver up to date?
Does turning off »Use Graphics Processor« in the Performance Preferences and restarting Photoshop have any bearing on the issue?
Are Photoshop and OS fully updated and have you performed the usual trouble-shooting routines (trashing prefs by keeping command-alt-shift/ctrl-alt-shift pressed while starting Photoshop after making sure all customized presets like Actions, Patterns, Brushes etc. have been saved and making a note of the Preferences you’ve changed, 3rd party plug-ins deactivation, system maintenance, cleaning caches, font validation, etc.)?
Note that the solution is to reinstall the OS -- because the problem is apparently some file missing or altered in the OS.
Yes, I went through the tedious effort of reinstalling (and then updating
to get current) the OS and it did finally fix it. So much for MacKeeper
being a good idea. Thanks guys...