Client dropping without disconnect?

[Kikinaak]

This ones got me scratching my head. I'm running the server on a lan and all works great for logging in and playing, but we are having problems getting disconnected. When this happens, the client appears to still be connected, but doors do not work, NPCs cannot be interacted with, and mobs cannot be fought. But the client never throws a timeout or disconnection message, it just lets us wander around the zone aimlessly.

/camp does not work, but /quit will get us back to the login screen. From there we can log back in, and be somewhere in the zone we were several minutes before noticing something was wrong.

This only appears to happen in gfaydark, it has not yet happened in any other zone that we know of. We have 2 other machines playing and it happens to both. Server side there are no disconnection messages or any hint there is anything wrong, and the same zone server takes the "new" connection. We are playing on a lan so I've ruled out latency issues. Any suggestions on where to look next?