It's a little confusing.

After upgrade to unity, I configured media keys through the unity settings gui.

Volume control (up/down) worked fine. It behaves fine.
Media keys (next/previous) isn't working.

Unsure about the lingo, but if seems like the actual keyboard shortcuts are registered fine, but when I use the unity gui to set media keys, which I believe involve DBUS/MPRIS, the media application don't receive anything.
For the sport of it, I have verified being able to control e.g. Spotify by sending DBUS commands in terminal.

How do I make media apps receive the appropriate command by using gui?
(I realize I can manually set keyboard shortcuts for each app separately. It would be a contrived solution. At any rate, I'm also interested in learning about my desktop environment.)

Thanks in advance.