This is a reversal of the position taken in RFC 2518. There is controversy about whether it also is intended to apply to cases where a resource is moved to a location where the individual resource is locked. The intent was that 7.7 would override these statements for the particular case where a resource is being moved to a locked location. Geoff favors getting rid of Depth locks, so that we would only have to be concerned about singleton locks. Servers are allowed to use whatever algorithm they like for generating lock tokens, as long as they are guaranteed unique for all space and time.
Depth locks across servers are problematic.
Think about moving a tree that spans multiple servers. ClearCase does bring lock along. Binding semantics maks it harder to say that the lock disappears. RFC 2518 lets servers decide how they want to structure lock tokens, as long as the token is guaranteed unique. So the destination server might not want to use the original token.