Don't replay metadata when the old source produces a new metadata chunk. This might be tricky because the old source might first produce an end of track, then a new track with metadata. Not replaying means leaving the end of track "undocumented". But most users don't expect and notice that end of track anyway. Perhaps we also need to find a better way to skip in switches?
Also evaluate whether the refined replay_metadata behavior fits all situations, in which case one should consider removing the parameter from switch operators.
More details: http://firstname.lastname@example.org/msg01967.html