I noticed that on the Spotify desktop version (Premium user, 18.104.22.168.g19de0aa6) for Mac OS (Sierra, 10.12.1) there appears to be an issue with the close / minimize / maximize window buttons. Specifically, the close / minimize buttons (red / yellow) are displayed properly, but the maximize button (green) is located all the way on the bottom of the window.
I've attached a screenshot. Minimizing the window and subsequently bringing it back by clicking the Spotify dock icon does not fix the issue. Maximizing the Spotify window (using the misplaced button) and minimizing it again afterwards does.
Hope this helps!
EDIT: Messed up the category and can't move or delete. Sorry about that!