In my experience, the bugged inventory slot is always only 1 square. When attempting to drag any item into that slot, either from your vicinity or from elsewhere in your inventory, nothing will happen. This occurs for both one-square or multi-square items that may touch the bugged inventory slot in any way.

Can confirm at Willow Lake, there is no loot. Very unlikely it had been looted each time, as it's in such a remote location.

I can confirm. In my case, I was walking through an inner doorway connecting two rooms with a splitting axe in hand. Clipped through the floor and was stuck in the basement (screenshot), but I managed to walk over to a stairway and clipped back into the normal area of the house.

In my experience it wasn't always impossible to strafe through doorways. It just varied as to whether you pulled it off on the first try, had to adjust awkwardly, or gave up and just walked through normally. I can't speak to the issue of strafing between beds, however. Ultimately, strafing through doorways is going to be really important as a player wants to observe his outdoor surroundings just as he enters a building to ensure no one has followed him.

Confirmed. I heard zombie sound effects that would not stop. Literally endless loop of different zombie noises. Nothing to be seen. When I stopped I began getting attacked, but taking no damage. After moving, the invisible zombie would have to catch up to me again to continue attacking. Still took zero damage, but vision became blurred. Finally I glitched through the floor of the supermarket, but unsure if that was in any way tied to the invisible zombie glitch.