A client with threads set differently form the server desyncs instantly.
Known problem, but it is not a bug. For some reason this is intended and is part of how the multi-threading for game state works.
I have now fixed this to the extent that the server will now override the local setting for threads when the game is connected to a server, and thereafter until a new game be started or loaded. This means that having a different setting for threads will no longer result in a desync.