There's some inconsistencies with the layout of some of the sets in regards to interiors and exteriors, and I don't just mean how you can see blue sky (and occasionally a tree) outside Ernie and Bert's windows. But like, take Hooper's Store for example: inside, on the other side of the door, there's a little booth, however that booth can't be there, because it would block the door that leads to Bob's apartment upstairs.