The other night, playing Species Deathmatch on a dedicated server, I tried switching to a team that had available slots to help even out the teams, but the game wasn't registering my attempts. After a couple games, after another dozen clicks it switched to another team, but retained my previous species (predator) graphic. In game I was a marine though. After that game ended, I tried switching to alien, but the same issue occurred.
Basically the bug is not being able to switch to teams on a dedicated STDM server despite available slots. I don't know if this was just a one time thing for me, though, since it only occurred on the last server I played.