side note, that inherit block looks strangely kinda cool with that shading (from dragging a block over it), kinda gives it a 3d affect
which browser version and OS is this? I can't reproduce it myself...
This is an issue that both @petermathijssen and I have had for a while (We both use Linux)
It's just a minor irritation as far as I'm concerned
very minor 
Chrome, ChromeOS. This is the first time it's happened to me. It no longer happens.
For Chrome and its siblings, you may try to disable "Accelerated 2D canvas @ chrome://flags".
Will give that a go and see what happens 
Yes, that did it. Thanks 