This one was tested yesterday, version 12, and Karl kind of got away. Ordered him to join group, but he didn't join our group...
Called for extraction, the heli did a touch'n go....1/10 th of a second. We didn't make it inside he heli.
You need to be close to Karl to release him. Once he is released he will become part of your, you should see this if your the leader. Its your job to keep him safe, each time you respawn you may need to give him a new order as the old order is sometimes lost. Mark sure you arm him as well and what we did was simplly sent Karl to a safe spot on the map and then told him to stop. When we were done in parisio and cleared the next objective, we he had him walk up to our location. Same thing applies to captives.
We had the same issues with the helo touch n' go. 1 in 5 times it would work, I suspect if karl is dead the helo won't stay around. Luckily fleepee added the secondary extraction point.