I had my M4A1 selected and I used the 'tab' to view the inventory. The, I choose 'drink all' on my 'damage' water bottle with 67%; I saw the survivor load the bottle into my M4A1 as a Mag, and then drink from the bottle. However, he did not drink at all, as the bootle was still full at 67%.
So, I clicked 'cancel current action' and 'drink all'. When he finished to drink the bottle, I saw items spawning into my inventory and I noticed that they were M4A1 attachements. I looked at my M4A1, and I discovered that it was replaced by a SKS.