Twice now, my vulture army has been unable to attack AI spartan that has stolen one of my vultures. First time was normal AI, second time was heroic, so that probably isn’t a factor. First time was Cutter enemy, second time was Anders. Both times I was Isabel.
I was still able to shoot vulture missiles at the hijacked vulture, but I could not attack. The second time it happened, I jumped my own spartan out of her stolen vulture, and she could then attack the enemy’s stolen vulture and then we could kill the enemy Spartan.
I have the PC version.