I am going through the same thing with my bitch here REW mate.
she will retreive to hand all day long with tennis balls, rope toys, canvas dummys, rabbit skin dummys you name it but as soon as she gets hold of a rabbit she runs all over throwing it about and then eventually she will come in close but always drops the rabbit short.
its as annoying as feck so I would also welcome any advice from the more experienced members among us
thanks