Of the two choices, copy the reference or copy the target, copying the reference is the least amount of work for the server. Mark Day noted while the choices in the protocol should surprise the least number of people, it's not always possible to avoid surprising a signifigant part of the population. We have to be ready to make an arbitrary choice because we can't converge on the easy to use solution. Larry Masinter then proposed that the protocol specification document indicate clearly that copy is complicated, and that users will have different expectations of what copy means. Hence, locking the reference is the desired functionality for redirect references.
Direct references have their own set of problems.
One attendee noted that here are four possibile choices when locking a direct reference. Either lock the target, lock the reference, lock both, or lock neither. Neither is out. Like copy you can make very reasonable cases for all, and like copy the choices seem very arbitrary. Locking the target makes a lot of sense except that you could move or delete the reference.