When sending from one instance of MC to another, whether this is a client controlling a server (not sure why a server shouldn't be able to control a client, but apparently it's not possible as client zones don't appear on the server), or sending to an instance of MC that is a DLNA renderer, and you have multiple zones on the receiving instance, the receiving instance doesn't switch the zone even though you've selected it on the controller.
For audio this means that even though the audio plays, you cannot see the cover art or visualisation (i.e. the Display View) on the receiving instance unless you manually switch the zone on the receiving instance.
For video this means that the audio plays but the video doesn't, as you cannot see the Display View.
I was trying this in order to get around the confusing aspect of needing to set up multiple library servers on the network and having to connect to each one separately to control them - I was hoping to only need to connect to one "central" instance which can see all the zones on remote instances.