Please turn off the graphics processor from the Lightroom preferences and check if that helps.
Open Lightroom > Edit menu > Preferences > Performance tab > Uncheck the GPU > Restart.
Tried your suggestion and it happened again. It seems to start messing up after about a half an hour of use...any other ideas??
I've also just noticed that when I review my system information that the real and virtual memory used in lightroom is steadily increasing even though I'm not doing anything.
Update to Lightroom 2015.9 or 6.9 that was released today. A memory leak problem like you describe was fixed.