By now most people are familiar with the fact that the dispkay cases you add to your home(s) in Hearthfire do not work automatically. You can open/close them, but you can not equip a weapon and have an option to put it in the display case.
If you want to put something in a case you have to drop the item, pick it up without adding it to your inventory, and then wrestle it into place.
My question is; are the display cases safe? I have read that items in thouse will re-set to default after a few days, destroying any items you placed in the process. Will I come home one day and find my priceless collection of claw-keys gone?
depends on the items you put in the displays cases. so far books are good to put in there and certain weapons like dragonbane. however I did loose a valuable sword from putting in those cases. try testing each case by putting an iron sword or something to see if it's ok.
Display cases, weapon racks, and containers are "safe" (maybe not due to glitches). "Loose" items in the house will reset after 10 days of the player being away from the location. Items in display cases and weapon racks *should* be fine.
I would always say test them yourself with items you don't mind losing my PS3 Lakeview seems to work fine placed things stay where i put them (the second time) items stay in the racks and cases with the cases things do move around a little (annoyingly) but other people aren't so lucky. Items with more unique shapes like the Nightingale Blade or Rueful Axe will often fall though racks and cases (see their pages bugs section).
Hearthfire display cases are not a container but more like a solid object, so they don't "reset" unless the whole house resets, which can't happen unless a crazy bug takes place, because the homestead cells are set to never respawn. You might find the display cases open after a long abscence, but the contents are still there. Tested with weapons, ingredients and gems.
About items resetting, I think it refers to items you find already placed. For example, in the first room you build in a homestead there's a table with a wooden plate and a rabbit haunch on it. If you throw them on the floor and come back many days later, they will magically be on the table again. Now if you also place something on the table where the plate was, when the plate "resets" it will displace the item you placed and possibly make it disappear. If you want to put an item in the plate's place, pick up the plate to the inventory first.