I just finished decorating my home. I filled display cases with everything from weapons to cool looking alchemy reagents. I left and came back and it looked like a poltergiest had moved in.
I have always had this problem with owned homes but i thought maybe it would be different in Hearthfire, guess not.
Oh well, usually after everything glitches and flys across the room or ends up in magical void areas hidden within the walls.. I can put everything back where it was and it doesn't happen again. Only seems to happen once with each item.
I got alot of work to do with all I have in this house though =[
If you want to start home decorating in a big way, dump all your desired items on the floor (preferably where someone is not going to walk through them), leave the house and come back, they are yours to arrange with no poltergeists. If you re-add them to your inventory you have to do the same thing before you can place the item. Just keep in mind that some very rare items were never meant to sit out in the open world and will be determined to sink through everything but the floor of your house, there are not very many like that though, they are mainly rare drinks and potions.
Most weapons you do not have to do that for, but it is always best to be sure than have to chase your stuff all over the floor.