Please provide your game logs.
I've just had this problem 8 or 9 times consecutively. Then when I got into a game players kept coming up as joining and then leaving immediately. They were already deserters so they won't be happy bunnies.
I am one of those unhappy bunnies
My computer was reset because of software issues so when I downloaded the game it would be as if I did for the first time. I had the same problem mcscouse has and it got me categorized as a deserter. (I tried it twice so that's how I became a deserter). I left the game and came back to it in a while and the bug was gone. It isn't a problem (for me) as long as it doesn't happen ,but I'm sure it would be a problem ,to a complete beginner who just downloaded the game for the very very first time. Here is the game log file so that maybe you guys can fix it for good if it isn't already.
Customer support service by UserEcho