[I GOT A VIDEO ON IT'S WAY THAT SHOWS THE PROBLEM]
Me and my brother sit behind the same router and 90% of the time when we want to play on the same server whoever tries to get in second makes the first one lose connection to the server.
Not only does the one that got in first lose connection but the second one actually never gets to get in the server either, getting the "Waiting for host" message indefinitely.
We originally had the same problem in the mod and we thought it was an Arma2 issue but this continues to happen in the SA.