Well, I tried sending some captured pirates from away mission map to my colony base via transport pod and found out they lose their prisoner restrains in the process. It results in that they are showed as hostile, not as prisoners. These hostile pawns do not have any program to attack, fight or retreat, they just wander around doing nothing, like they do when caravan stops for random encounter. But I can't make my pawns take them to prisoner beds or arrest them. Only shoot to death. I figured out it's a bug and wanted to report it just before but found the same exact two reports with answer the bug had been fixed:
https://ludeon.com/forums/index.php?topic=46175.msg438995#msg438995
https://ludeon.com/forums/index.php?topic=45915.0
So, my question is: is it only me or someone else still has the same problem.
I noticed this in my last game, but I was able to recapture them. I can't recall if I had to beat them down first or not.
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OK, just tested it, yup, same behavior as in the first link you suggested. The pawn arrives as hostile and unrestrained. You can down him but population control usually kills him. If you do succeed in not killing him, he can be captured as usual.
I didn't test if it happens with other factions, but it definitely happens with pirates.