The file /usr/share/applications/listen.desktop contains a line
MimeType=audio/x-musepack;application/x-musepack;audio/musepack;application/musepack;application/x-ape;audio/ape;audio/x-ape;audio/x-mp3;application/x-id3;audio/mpeg;audio/x-mpeg;audio/x-mpeg-3;audio/mpeg3;audip/mp3;audio/x-m4a;audio/mpc;audio/x-mpc;audio/mp;audio/x-mp;application/ogg;application/x-ogg;audio/vorbis;audio/x-vorbis;audio/ogg;audio/x-ogg;audio/x-flac;application/x-flac;audio/flac;
which should read
MimeType=audio/x-musepack;application/x-musepack;audio/musepack;application/musepack;application/x-ape;audio/ape;audio/x-ape;audio/x-mp3;application/x-id3;audio/mpeg;audio/x-mpeg;audio/x-mpeg-3;audio/mpeg3;audio/mp3;audio/x-m4a;audio/mpc;audio/x-mpc;audio/mp;audio/x-mp;application/ogg;application/x-ogg;audio/vorbis;audio/x-vorbis;audio/ogg;audio/x-ogg;audio/x-flac;application/x-flac;audio/flac;
