Entering buildings

[RickApple]

Has anyone figured out why it is upon entering a building with a soldier, some buildings will then "remove the roof" to reveal the inner structure, while other buildings roofs do not "go invisible" in this way.

I have noticed some buildings will show the "load" icon when you move over the door (green rectangle with gold trim and gold moving arrow), but this does not mean anything with regards to the issue at hand here.

TIA

Rick