Alternatively, have three arrows, one parented to bow, one unparented for the flight, and another parented to the target, and change the visibility at the appropriate times.

To illustrate my point, there's a tuorial over at the e frontier website in the poser animation section, looking at this exact trick. They use the problem of making someone take off their hat (parented to head, and then to hand), but it's the same principle.

JonTheCelt