Introversion

Was in a server lobby with Xander, he was just about to leave, said bye, then it said Killjoy has left the game.

So some kind of bug that got the clients mixed up?

Server was

Dedwinia Test (Owner: bert_the_turtle)
The Apex of Infinity was the map that loaded when he left.

That's normal. You moved from one player slot to the other, and to your client, you left and rejoined. The chat SHOULD have looked something like this:

xander left the game
killjoy left the game
killjoy joined the game

Yep only think is that it didn't say I had joined the game (rejoined) I could just keep typing.

Thanks anyway for the heads up.

Yeah, I've experienced this as well, but I'm guessing the client just doesn't keep up with events in the chat window, since it seems to work just fine after.