I was playing the SoaSE Diplomacy 0.90 beta over LAN with two friends and about 3 hours in we noticed one of us had an entirely different experience from the other two.  The host and I shared the same experience but the third player had entirely different stuff going on in the universe.

We could see each others ships in phase space and the would arrive in the same spot on each screen, but the engagement in the gravity well was completely different.  The most bizarre problems were when the computer attacked him and on my screen he lost all his ships and his planet, while on his screen he saved the planet only suffering a couple losses and no planet damage.  He also captured a planet and the host and I only saw it controlled by the computer.

For the most part the odd man out saw the shared universe correctly, just about a minute after it happened.  The experimental weapons always fired at different point between the 2 systems.

I know we were in the same game because I could offer him missions and chat with him.  We developed pacts and such.  The only other difference between last nights game and others is when the fleet sizes started getting over a thousand population each the game did not lag nearly as much as it has before.

The computers were a toshiba running XP, a new macbook pro with windows 7, and another 2-3 year old macbook pro running XP.  The windows 7 machine de-synced.