This has been a problem for as long as the mode has existed. If I start as the goalie and one of my team mates decides he's going to play goalie I'm now in a position where I have to guess if you are going to stay on goal so I can go help my other team mate.
But they never stay on the goal if I leave it to them. So now we have two people on goal because the person wanting to play goalie is getting scored on. So again,if you don't spawn as the goalie please go help our other team mate on the field. /end rant