I just (finally) got a keyboard with proper media keys but Spotify seems to be breaking them.
So long as Spotify isn't open, media keys work fine. Mute, open mail, etc. When I open Spotify, hotkeys initially work fine, including play. Once I hit play, whether by clicking the UI or by hotkey, the first hotkey I press is repeated as if I held it down. If I hit volume up, it goes all the way up. If I started playing with the Play hotkey, it plays and wont stop. All other hotkeys are disabled so long as this one still thinks it's held down. The key thinks it's held down until I close Spotify. This bug happens whether or not Spotify is focussed, and still occurs after disabling the play overlay. The input overload sometimes causes other keyboard issues, like other keys intermittently repeating as I type.
Other applications (Windows Media Player, etc) seem to work fine. Reinstalled Spotify and updated Keyboard drivers. Restarted computer. Keyboard is a Microsoft Ergo Keyboard 4000.