Geoff claims that rfc 2518 says nothing about whether a URI that identifies a locked resource can be changed to identify something else while that resource is locked. There appears to be confusion about whether references are themselves resources or whether they are just alternative names for a resource. References to versioned-resources are more complicated than other references. Applying a lock to this reference is in conflict with the basic purpose of these headers, namely to select a different revision when appropriate. Thus a definition of locking that requires locking the reference would be incompatible with the way versioning uses references to versioned-resources.
More discussion is needed.