The NPCs will eat the content of the can without even opening it. Once the can is empty, it remains a sealed tin can that can’t be used to can food again.
You should post this as a bug on the bug tracker on github unless it’s already there.
Nevermind its already there. However I am unable to reproduce this? I spawned in a NPC made them my friend and then gave them a food can. No can was left in their inventory or in mine… Also when editing them to be able to pick items up they wont pick up canned food. So I gave them a backpack and gave them a can. Also no empty can being generated.
At this point I cannot reproduce what you did. Can you let me know the sequence of events that caused this and also what version of the game your running?