This a long standing issue. Here i what I think the current situation is, in general terms, although I have no direct knowledge.
MC only has easy control over its own system and has added various timing parameters to try to do the syncing. However, it does not have direct feedback from each of the zones. It needs that to do precise syncing. It is hard to sync something you do not control.
Sonus does a good job of synchronizing, but they have direct communications between the nodes under their own control. There is also some thought that their synchronization breaks the bit perfect model.
Bottom line - Matt knows about the issue but given it would take a significant effort to establish the feedback needed for precise syncing, chances for a fix are not good. But it is good to raise the issue on a regular issue. I believe Matt is open to fixing this, if he can figure out a good way to do it, without a huge development effort.
That's my best guess. If anyone has better information, I would be glad to hear it.