okay, upon some further research... I've found a few things...
A) The Postal Inspector needs no warrant to open a package if they find it suspicious. Sometimes they tear a corner so that drug dogs can sniff.
Wrong, Priority mail needs a warrant to be opened.
B) The post office has antiquated sorting machines that can sometimes rip open packs and envelopes. It is possible that this happens, the bottles fall out of the packs when they are on the conveyor or when they get dumped into the roller. Once it's out there is no way to tell where it belongs.
It's possible, but doesn't happen that often. when it does happen the put all the pieces, including the original envelope/package into a new package w/a letter
C) Someone knows what they are looking for and are really stealing and stocking up on need2 products. Although from what I understand, for a postal employee to do so, they could get 5 years in jail per incident. Not a risk most people would take to jack something worth $50.
Not to mention they're paid pretty well to start with, and it's a retarded risk.
It's fucked up nonetheless... Although I lean towards reason B as the real situation of what is going on.