[chrispedersen]

Let me ditto Sombre's advice:

The replay bug occurs WAY more often if:

a). Host and client are on two different systems.
b). rollbacks are involved.
c). Patches have been applied mid game
d). Someone does not have the same version of the game 3.23b for example.

I do wish there were a way to validate clients before a turn were submitted (and no, I'm not talking about the -v option).