Thanks to vals for pointing out the GPU aspect… This reminded me of this CSS-Snippet which tends to solve Chrome rendering issues:
-webkit-transform: translateZ(0);
I’ve applied this to the container (div.post) containing the problematic item (i.icon-) which has a fraction width, problem solved!
Credit: I’ve got this solution from this answer to fix incorrectly rendered (fixed) elements after navigating to an page anchor.