I used the rescuePOWS.sqf which you can easily find on Internet.

the rescuePows.sqf contains, between other, the following line:

{[_x] joinSilent _ldr} forEach _grp;

I wanted to rescue an heli pilot but it seems that doesn't work.
So I created both a civilian named civil and a pilot named pilot, initialized in the same way.

this addAction ["Rescue POWs","rescuePows.sqf",[POWS],1,false,true,"","(_target distance _this) < 3"];

My player contains the following init:

POWS = [pilot,civil]

When I perform the addAction on the pilot, the script is correctly called but the joinSilent doesn't do anything.

When I perform the addAction on the civilian, both civilian and pilot are included in my group.

Any idea?