Agree with this, in the past I've had dogs on their way back to me with a rabbit when another rabbit gets up infront of them, they run a bit with the first rabbit in their mouths before dropping it and taking off after the runner. They might or might not catch it but the original rabbit being alive has hit the ground running and is gone.
That said a mate had a dog that done it when ferreting if two rabbits bolted together, he'd kill the first then was straight onto the second, that said he never retrieved any of his rabbits.