The SE icon on the left hand side of the top bar disappears when you hover over it on Unix and Linux:
Idle (hard to read and almost invisible):
I'm not sure if any of the current icon behaviors are intentional. Are we supposed to see a big square appear around the element when we hover? Is it really by design? And I really don't know if any of the colors are intentional since I have a lot of trouble reading the colored text on a black background on all of the various sites I tested. But I'm pretty sure that having it disappear, at least, is a bug.
This may or may not be the same issue as Odd red SE logo on New top bar.