I just installed the latest NVIDIA driver (v 372.54) for my graphics card (GeForce GT 630/PCIe/SSE2 OpenGL). Perhaps coincidentally, I've noticed my LR (CC 2015.6.1) display is intermittently flashing blocks of pixels over my image as I move the cursor.
Well, I figured out how to roll back the NVIDIA driver. I'm now back to v 368.22 and the problem described has disappeared. I guess I'll leave it here for a while.