A door placed on an inside wall looks normal on both sides. A door placed on an outside wall looks normal from the inside, but the glass is missing on the outside. This only happens on the Magic HQ lot and a lot in Forgotten Hollow (though I haven't tested every lot.)
Here's what a door looks like placed on the Glimmberbrook Watch look:
Outside view:
Inside View:
And here's what it looks like on the Magic HQ lot:
Outside view:
Inside view:
It also does this for some other glass doors (not all that I tested, but many of them).
Here's one door as it normally appears from the outside:
Here's what it looks like when it glitches:
It's a more subtle difference, but the normal door has a slight tint to it, and you can see light reflecting on the glass when you move the camera around. In the broken door, it looks like there's not glass at all.
