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Try going to System Preferences, Displays, then changing the resolution to something like 800 x 600, then immediately changing it back to your normal resolution.
 
Try going to System Preferences, Displays, then changing the resolution to something like 800 x 600, then immediately changing it back to your normal resolution.

I've had this happen and this definitely works.
 
Yeah the resolution thing is actually what I tried right after posting - stupid of me! That option click tip is invaluable though.
 
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