When playing multiplayer, my friend and I have slightly different perspectives. What I mean by this is that we would see different amounts of ships in different planets. It starts off with only a few planets but eventually the game gets unplayable as we don't know who's perspective is correct.
Here is an example. I see a planet and there are like 5 enemy ships on it. No big deal for the 15 of my ships that are there too. However, my friend sees 60 enemy ships there and is losing a battle there himself with his 30 ships. Mine are nowhere to be seen on his and his are nowhere to be seen on mine. We can even both think we have the same planet.
I'm not sure if this only occurs on large maps but we usually play maps of the size of Triumvirate (medium or large, i think) and we'll play with 2 - 6 AI on 2 person teams. Both of our computers are pretty good.
This has occurred in every game we've played together of the beta (4, i think).