gst-plugins 0.8.6 include a musepack plugin and this plugin compiles flawlessy,
but both totem and rhythmbox hang when I try to play .mpc files. I noticed that
playing .mpc files with

gst-launch-0.8 filesrc location=file.mpc ! musepackdec ! alsasink

works, but if I try 

gst-launch-0.8 filesrc location=file.mpc ! spider ! alsasink

I get only

 RUNNING pipeline ...

** (process:18352): WARNING **: deadlock detected, disabling group 0x80afae8

** (process:18352): WARNING **: deadlock detected, disabling group 0x80afae8

** (process:18352): WARNING **: deadlock detected, disabling group 0x80afae8

** (process:18352): WARNING **: deadlock detected, disabling group 0x80afae8
Execution ended after 2 iterations (sum 1151345000 ns, average 575672500 ns, min
245000 ns, max 1151100000 ns).

A similar error (disabling group 0x849e0f8) appears if I launch rhythmbox in
console to see the output, then program hangs.