Network.Instantiate causes "WriteLock is still acquired. Procedure call skipped to avoid a deadlock!"

In my code I have a spot where players each Network.Destroy their old character and then Network.Instantiate their new character.

When I do this I get the error:

PhsicsSDK: NpScene::setGravity: WriteLock is still acquired. Procedure call skipped to avoid a deadlock!

Before upgrading to 4.1 this would simply crash the unity editor.

I've tried replacing Network.Destroy and Network.Instantiate with my own RPC functions but then GameObject.Instantiate causes the same error.

I've also tried making an RPC that just sets a flag telling each player to do the instantiate on their next Update, thinking that maybe the instantiate was happening at a "bad time", but the results are the same, exact same error message.