So you're telling me that the stuff gets un-arranged as soon as you leave the house? I've left some things spread out (239 items to be exact) in the same spot, I just spammed "drop item" and they haven't moved yet. but what you're saying is that if I took the time to arrange them it would become a mess again?
Here is how it happens. Each item as a "Clipping outline" (not the right term, but it's what i am using here) that denoted the outer boundaries of the object. This clipping outline keeps one plate from merging with another one if you put them next to each other. So, you line up all your stuff and it all looks neat.
Then you leave the cell and come back at some point. Two things will happen, either the game will try to reset all the stock objects in the cell which can knock other objects off the shelf. However, this is not as big an issue as the other reason. When you enter the cell, all items in the cell are rendered again and placed where the game remembers them being. However if the placement was just a little off, then an item can fall or drop. If the item was not flat on the table, then it can tip when rendered. When it does this, the clipping outline can bump into another object which can set off a chain reaction of things being moved around the cell.
It was even worse in Oblivion and Fallout 3 when they first came out. I could bump into a vase, and everything would explode all over the room like a popcorn popper. They adjusted the physics to reduce this in those games. They got item placement pretty good with this change in FO3 and FONV. But, as one poster above said, the ways to spin the obkjects or flip them has been taken away.
I think some people are saying that you need to do it like this:
Enter house.
Drop stuff.
Leave house.
Save.
Exit Client.
Open Client.
Reload.
Enter house.
Decorate.
I think it works if you go like that.
This works as the game somehow treats objects that are rendered in the cell, then later moved, differently than items that are just dropped in place, then rendered again at a later cell load. Items placed this way seem to get moved less when the cell renders. They can still get bumped around, but it does make for a more stable item placement.