GPU preview glitch
I encounter this glitch since introduction of GPU preview.
Only now I managed to narrow down the conditions to replicate it.
When the Control pane is switched off (Window > Control), and Screen Mode is in Fullscreen Mode with Menu Bar, then when the working area is scrolled down, black horisontal lines appear. As if they are somehow traced by the top edge of the working area. Once I zoom out/in, they disappear. Also switching to CPU preview removes the glitch all together. This appears on both retina and non-retina displays.
This does not happen when the Control pane is visible. Or the Screen Mode is in other modes (Normal or Full Screen).