My ds (5) is a personal space invader. I try my best to keep him in line, but I think he thinks that the 6 inches further that he stands will get him to the ride faster. Sorry about this! I always say something to him about it. This is my normal spiel:
Ds are you with that family (the one he is invading their space), he normally responds no, than I say then come back with us please.
He will come back with us, but he tends to normally creep back up and almost every other line we get into - the same thing!
Sorry again - we are in training right now!
Just for the records, I can't stand personal space invaders. (Makes me think of the Seinfeld episode with Judd Hirsh - I think it was him.)