Whenever I zoom in/out or make an adjustment (curve, contrast, etc), the preview appear to be darker for a moment before it shows the correct preview.
I'm not sure what causes this problem. If I disable GPU acceleration, there is no flickering. Before 2015.5 release, everything was fine and also no flickering.
Lightroom CC (2015.5 release)
MacBook Pro early 2011 (OS X 10.10.4)
Core i7 2.2 Ghz
AMD 6750M (1GB)
I use external display with thunderbolt HDD in daisy chain (mac -->thunderbolt hdd-->display)
It's a known problem with the 2015.5 release: Lightroom CC/6: Annoying acceleration flicker glitch | Photoshop Family Customer Community..Please add your vote and opinion to that topic, to make it (a little) more likely Adobe will prioritize a fix.