I had this happen a couple times tonight while I was playing Ground War: I was already in a half-filled lobby waiting for the timer to count down when all of a sudden I was warped directly into joining a game in progress. I didn't leave the lobby, didn't even start to leave it, there wasn't a host migration or anything like that...just normal countdown + searching for players & bam: into the other lobby I go.
I can deal with being thrown into games in progress when I'm just joining a lobby, but without even asking for one? Very annoying, particularly when the game/map you actually want to play is leading the votes and then you get TDM on Turbine instead.
Also, what's up with the Ground War lobbies resetting the teams (and final countdown) every single time any player leaves or joins the lobby? I've never had a match start in that playlist without at least 4 reshuffles, and it's gone as high as 10 before. If that's the fix for the "need more players to balance teams" bug then it still needs some fixing.