I suspect that has do to with what the game consider as an "Item"
In the teleport and feather fall's description it says it works on "Items" as well, but only works with chests, barrels, crates... Not those items that you say (skulls, shells, keys, weapons)
Just my two cents tho.
Good two cents.

I think this is hard coded (which item is an "item"), unfortunately. I tried messing around with ItemHandle and ItemTemplate but still no luck...
I also tried to use
CharacterPickUpItem(_Item) in a script action but it wont work either. Strangely on no item tho...