Who said anything about a back door?
Let's look at it in relation to the car parking spaces. Starting from the ones closest to the wall with the farm mural painted on it, the door on the left is in line with the 2nd and 3rd car parking space whereas the door on the right (the ones the toys first enter) is in line with the 5th. When Buzz comes out and runs across the car park, Zurg breaks out of his box and starts to chase Buzz.
If you look at the shot when Zurg is chasing Buzz across the car park, you can clearly see them running across car parking spaces 2 and 3. This can only mean Buzz left from the other door, not the one the toys entered. Therefore, there would be different stuff around this door than the first one.
"I'm Kent Brockman, and that was My Two Cents"
OK, looks like I'm going to have to explain this one. When the toys are in the trolley, you can see both door's along with two of those rubber pressure-sensitive mat's on the ground that open them. The toys watch that bloke walk in at the beginning, cash registers 3 and 4 are opposite the door. When Buzz is trying to get out, cash register 2 is opposite the door (You can see it when Zurg is breaking out of his box) And no, Kirkly, Al's apartment isn't opposite the door Buzz exits by, why else is Buzz running on an angle across the car park when he leaves the toy store instead of running straight out of the door and across the road.
They don't come out the same door as they go in. The door they enter in opens up to the cash registers where as the door they walk out has a display with baseball bats and stuff opposite it (Buzz has to jump up on all of it to grab that monkey toy so he could follow Al)