Save file: https://drive.google.com/open?id=0BwyJCiTrsB4SeGNrRW9TdkRnckk
Player log: https://drive.google.com/open?id=0BwyJCiTrsB4SNXFMMFVwajJxWkE
I had a sapper raid at the same time a slayers trader arrived (without slaves...again...), captured a raider and sold for free to the traders. Once the captive leaves his prison cell to join the NPC caravan, he walks towards my food supply. I caught him before the act (pre).
What would I expect?
Since he is no longer part of my colony, he shouldn't be feeding freely and should be fed by the other faction instead.
I think this is WAD, or at least it seems to fit the following Mantis report, and therefore Tynan's comment about pawns from other factions eating player's food being WAD seems to apply here (as when you sell a prisoner to a slaver they become "from another faction", and therefore able to eat your food regardless of your wishes).
"It's not a bug, pawns from other factions don't respect player AI directives." Tynan (2016-08-31)
https://ludeon.com/mantis/view.php?id=2627
I'll leave this open just in case there is something going on here that there shouldn't be, but my guess is this isn't a bug.