I just went to my home in Markarth to drop off a bunch of nice masks and flawless gems. I placed them all on some bookshelves. When I came back a few days later they were all over the floor. I tried it again with the same result. Is it my wife Hroki? If it is...............

If you want stuff to stay where you put it, you have to drop it, leave the house, get a bounty and pay the fine, then return to the house and move it where you want it. It's a bug. Here's a really useful thread with more advice on how to get stuff to stay where you place it:

http://www.gamefaqs.com/boards/615803-the-elder-scrolls-v-skyrim/61718366

Sometimes when cells load stuff goes berserk.
If you put it all back it may, or may not stay there.

I usually put big things like tusks or troll skulls on top of the chests in my bedroom and they have never moved.Other things do though.

Apparently every house you can own sits directly on top of a fault line. I remember taking hours to painstakingly put stuff I'd collected (Dwemer stuff, weapons, and other various items from quests) to give Proudspire a nice personal touch. I made the mistake of the taking pre-existing cups, bowls, and other decorations off the tables and shelves. The next time I came back the stuff was everywhere. And that's the way it stayed. The house I'd spent some 38K on was a mess.

This is why you often hear noises when you enter an area: stuff that had been positioned by the developers, falling or flying from where it had been placed.

You don't have to get a bounty and pay the fine.... Just drop an item, leave the house, reload from the autosave, walk back in and put the item where you want it. Works every time....

Some stuff, if left in close proximity to each other or other items, suffers from "havoc jitters" that can send them literally flying off the shelves. Some objects are simply so obtuse as to never settle down and stay put. On my first character, I placed a statue of Dibella on the shelf to the left of the bed in Proudspire Manor. It stayed put. On this guy, every time I walk through the door - even the basemant door - of Proudspire, I hear a hollow metallic "clunk". I head upstairs and sure enough, the statue is on the floor again.

So I carefully put it back. The next time I walk into Proudspire? "Clunk!" I tried putting it back and accidentally dropped it before getting it right. Stay there! I mentally projected. I turned around and as I approached the stairs, who should come running up but Jordis? Before I could ask why she was there, she said something like, "You dropped this. It would be a shame to leave something valuable lying around for anyone to take." I just noticed the note on the screen, "Statue of Dibella added." I turned back, looked into the bedroom... and the statue was gone. I had to drop it from my inventory and place it again.

The next time I came back to Proudspire? Yep: "clunk!"

Le sigh.

I've had very little problem's keeping stuff where I put it, the second time anyway. When I first get a house I remove all the item's that I know I will not want to be there at a later date, such as cup's, plates, food, wicker baskets. I don't drop them on the ground and leave them their, I drop, place ( not as carefully as I could) leave, come back in and replace the item even if it's still where I put it being more careful how it's placed. I've stacked book's on shelves once and they are still where I put them when I come back in. But I placed a Dwemer helmet on a shelf and after replaceing it about 20 time's, switched it with a different helmet and that one stayed where I put it the 1st time. ( same place ) I seem to be haveing the same problem with the "dragon mound map" It doesn't want to stay on the table.