Could you try running rhythmbox from a terminal with "GST_DEBUG=*:2 GST_DEBUG_NO_COLOR=1 rhythmbox" and seeing if any error messages are printed out when you try this?
Could you try running rhythmbox from a terminal with "GST_DEBUG=*:2 NO_COLOR= 1 rhythmbox" and seeing if any error messages are printed
GST_DEBUG_
out when you try this?