When two players attempt to get in the same vehicle position at the same time, one of the players gets stuck in the other person's view until their soldier is killed by someone. This bug is very annoying, it's happened to me several times and I see someone else complain about it almost every day as well.
I was hoping this bug was already posted here, but I searched for "merge" and didn't get any results, so I went ahead and posted just to make sure.