there must be an error with bethesda's item sitting stuff
everytime you set an item down in your house like to display and then come back the first time they are in the spots you dropped them from your inventory but you just have to grab them and put them back the second time and they stay put
then there is certain items that will fall back to the floor or move from there spot always when you set them up ex: glass claw, bust of gray fox,, honningbrew decantor, model ship
also all the dragon claws seem to want to move to the left or right slightly every few loading screens when you come back to the house and can end up meshing into each other
if this has been reported already sorry but it has been bugging me and since fallout and oblivion never had this problem ive always put unique things around my house which i bet most ppl do
to duplicate this bug you can buy a house clear off a table or something then drop an item you wish to display carry it over to a table or shelf put it there then leave your house then come back into the house and you will see it back in the area you dropped it.