Mapservered in Large Leagues

I am getting mapservered when a league I am in gets to a certain size, usually about 18 people. At this point I am getting completely cut off from any response from the server, my ping just starts to skyrocket and I soon get dropped.

If I am quickly quit the league when I notice the lag then my connection returns to normal.

I use a mac with bootcamp as well as play on the mac side and this problem only occurs on the bootcamp/xp side.