Here is how you can get a door to snap to the grid. Place the door. Move the endpoints on top of the grid intersection that you want it to snap to. It doesn't need to be perfect, but the dot should cover the intersection. (I'm not sure exactly how close it needs to be). Go to the dynamic lighting layer, and draw a line which snaps to grid on the same intersection as the door endpoint. The door endpoint should move to meet the end of that line. This is a bit of a pain, and I support the idea, but this is an inconvenient fix (which I hope will only be needed temporarily).