Sometimes when knocking items off of item frames, the item will bounce around, sometimes even bouncing through walls/floors. They can also disappear if it occurs in underground base if there's no outside or second floor. This can be also a major problem when it occurs with valueables, such as Enchanted Items, Enchanted Books or other goods.

To replicate, put any item in an item frame within a house. Repeatedly knock off and put back on until item flies through wall/floor/cieling.