In the Controls screen, all the key and reset buttons doesn't have the bottom outline. In the first screenshot, there's a closer look in the buttons, and in the second, there's a brighter background for better highlight.
I don't know if it's a valid "bug" or not - this is a minor thing, but I reported it just because all the other buttons have complete outline, and it looks kind of weird.
Confirmed, I would have never noticed that had you not pointed it out though.