I just wanted to see if this has happened to anyone else. I took 3 of the dragon masks I had collected and put them in a display case in my hearthfire home. (The one near Solitude. I can't remember the name right now.) For a while they stayed there however when I cam back to my house last night. One of the dragon masks were on the floor and the other 2 were completely gone. I have about 30 saves. None of them are far back enough before I put the masks in the case. Thanks for any help.

I thing you did it that way:

Drop the item on the floor. Leave house and re-enter. Then pick up item into display case. If you accidently pick the item back into inventory, you have to re-drop and re-enter house before placing in display case.

However, display cases are not the safest place to store items. Even if containers are more secure for storing items, most of those will respawn, If you leave the area for multiple days.

In most cases, 10 days, but the exact number depends upon where the container is located.

Any contents left in a container when it respawns will disappear and be permanently lost. http://www.uesp.net/wiki/Skyrim:Containers#Safe_Containers provides details on which containers can safely be used for long-term storage, without risk of losing your stored items.

Chests and furniture (not barrels) in player-owned homes should be safe storage. Items left loose... may be safe, but may glitch into the great unknown.

I've been using the jaxonz positioner, and I haven't had any problems once I lock items in place. At least, so far so good...

You can also duplicate the item with the positioner, which I generally do with priest masks, being careful to put the original in safe storage and the duplicate on display. I don't know that it matters, but...safe side ya know.

I put the dragon priest masks on their busts in the Dragon Priest shrine in Labyrinthian, except for Volsung which I wear for extra carrying weight increase. The Solstheim dragon priest masks I put in a chest or wardrobe or a drawer in my house.

If You are Lucky, You may find the two Masks somewhere around the display case.

I have an old Saved Game in Hjerim where I displayed a few Dragon Claws, and one of the Claws was clipped into the wall enough to fall through the wall and into the nothingness if I picked up another claw first.

If You are on the PC, Console Commands may be used to recover the masks. Using "tcl" can allow Your character to walk through an item and find out if the Masks are still in the Home. "player.additem" can be used to recover the Masks if They have fallen into the center of the Game World.