Maybe it's only a lack of logic but... well^^:

Say we have an item with a baseform A
This item is dropped on the world that means it has now
-A baseform (A) (0000aaaa)
-An objectreference ( B ) (ff00bbbb)

In a script, I save B address somewhere. (ff00bbbb)

Lets pick Up this item (A) , which is now in my inventory
with my script, i know B, and I delete B, papyrus doesn't raise any error and the object A is still in my inventory

If I drop A somewhere, the object still have B as objectReference.

Lets pick Up this item (A) again , which is now in my inventory again.
now lets remove A (delete it)

Does B still somewhere, and should I care about it? will it be garbagecollected? will the reference be reassigned to another item later?

My guess is that the items Objectreference changes when it enters a container and becomes managed by the container. Which would explain why you can't call member functions on objects once they enter a container. But it is simply speculation. Why dont you make a test quest with a player alias and register for the OnItemAdded and OnItemRemoved events and see if the objectreference of the item is maintained during the transitions?

This, but with the exceptions of persistent ObjectReferences (REFR) and quests' ReferenceAliases. Even non-persistent ObjectReferences will temporarily retain their REFRs' FormIDs, but they'll not be remembered accross save game loads/game restarts. Ghostblade, [REFR:00094A2C] (places dunAnsilvundGhostblade "Ghostblade" [WEAP:00094A2B] in GRUP Cell Persistent Children of Ansilvund02 "Ansilvund Burial Chambers" [CELL:0001F358]), will always retain its REFR FormID since it's persistent. http://www.creationkit.com/Delete_-_ObjectReference will only work on script created, save game or [FF] range forms and shouldn't be used on anything that's placed by a plugin.

Thanks, you two.
Yes I made some test but:
that was actually my concern, I was wondering if "empty" object reference would cause useless ref in save, and apparently not.
Thx!