Cursed my **bleep** off today when I tried to log my girlfriend out so I could listen using my account while she was out jogging and using here phone. I can confirm that navigating the dropdown menu with the keyboard works, but clicking the items with the mouse just makes the menu disappear.
There's also a ghost menu item between Settings and Log out (you have to press down twice to get from Settings to Log out).
Ubuntu 16.04, latest Spotify client installed (did an apt-get upgrade to rule out that it had been fixed already), standard 1080p TV used as display (aka. no HiDPI).
In summary, since not only Wayland hipsters are affected this is pretty serious, hopefully you'll fix it soon.
Same issue here running Arch Linux 4.9 on Gnome with xorg. I've also noticed that right clicking the right hand friend pane doesn't do anything and since there's no menu I can't find a way to hide it. This seems to confirm that there's something not functioning right with mouse interaction.