That is an excellent question Milli. I have seen this before too.
I think bellagio could answer this question.
I used to think that the staff needed a note from the guest to leave the resort with items, but staff at the MCC last year told me they didn't need a note.
Although I have seen the bags gone through, especially at BCV, I have never seen anything being taken out and not being put back in the employees' bags.