In all my heartfire houses the displey cases (both dagger and wepon) dont work. They work fine in other houses. The mannquins , weapon racks and plauqes work.

Is that a bug or intended? What i need to do?

They work as intended, so you can place what ever you like in there. A tip though, drop the item you want to put in there on the floor first, then leave the house and come back. After that you can arrange them as you like and they won't "fly out of the case".

I display books and dragon bones and dragon scales and bows and swords and what ever I like in those cases.

Yep, makes it a little more difficult, but they work.

Ahhh. The problem was that they don't have the activate option. If you just put items in there, its okay

Yea. you can also display armor in the large cases. I put my Legendary Ancient Shrouded armor in one of those in my Armory. Looks cool