I remember reporting a bug, a few years ago, though I can't find it now. It was about the weird glitches in the green icons next to the search bar in the toolbar.

These: https://www.dropbox.com/s/9umwphlisjy4uzd/Screenshot%202014-...

I included screenshots at the time. I got brushed off with a "this doesn't happen for me, it's probably your system being messed up" and my bug closed as invalid.

It's still there, across several different OS reinstalls. For that matter, it's still there in recent screenshots from other people: http://www.snapfiles.com/screenfiles/calibre.png

So maybe it's intentional? It seems too ugly for that, but...