Posting this just as information in case anyone would have the same issue.

When improving a player house I placed new weapon racks, standard ones, plaques (shield and normal ones) and dispaly cases (daggers and big ones). I set enable parents for them in order to be able to let the player buy the new furnishings like in vanilla.

Then I had the issue that I was able to place weapons but not to remove them. It was like that they were contained in the activator box. I could take back larger weapons by grabbing parts that stuck out of the (invisible) activator box, smaller ones would just be locked in.

Then, by testing, I found out, that weapon rack ACTIVATORS (orange boxes for display cases and standard racks, white boxes for plaques) MUST NOT have an enable parent.

As soon as I set their enable parents to none the problem disappeared.