Can’t find any other reference to this but I’m finding that if I’m playing a stream (http - either radio or streaming a podcast URL) then if I skip to the next track, or stop and then try to play a new track, mopidy reports that it is playing the new track but the sound that comes out is previous stream.
It looks like gstreamer hasn’t had something cleared but I’m not sufficiently knowldedgeable with gstreamer to interpret the logs.
Happens on macOS and on Ubuntu 18.04. Ubuntu 16.04 seems to be more reliable so I think it must be some recent gstreamer change.