mpd-0.18 dropped your keywords because of a new dependency on adplug. So please either keyword adplug and re-keyword mpd or mask USE=adplug on your arch.
Marked ~hppa.
~arm added.
sparc dropped
Heads up for ppc64: As soon as mpd-0.18.16 is stable, I will drop 0.17.x, so your keywords will be removed completely unless you keyword 0.18.x by then.
Fixed by bug 525846