Pidgin 2.6.4 + Musictracker 0.4.20 + Spotify 0.3.22 (r58364) when using "Messenger compatible interface", "Auto";

%a is always empty, no album information %r is "Unknown" (player information)

This may be a problem with Spotify not updating %a (Album) information, though %r (Player) suggests there might be a problem with Musictracker code.

I'm afraid the absence of Album information is due to Spotify not sending it.

The absence of the player identification information is a limitation of the "Messenger compatible interface": that doesn't transmit the player identity, so it is not possible for pidgin-musictracker to report it accurately. (See FAQ #6 http://code.google.com/p/pidgin-musictracker/wiki/FAQ#6)