Copying and rebuilding package from one PPA to another doesn't work

If you copy a package from one PPA to another, and choose the
rebuild option, the operation fails if the source version of the
package already exists in the target PPA. For example, if I copy
the jaunty yuicompressor from the ~launchpad PPA to another PPA, and
request it to be rebuilt for karmic, I get an error message about
the jaunty binary already being present in the other PPA:

"""
The following source cannot be copied:

    * yuicompressor 2.4.2-1 in jaunty (same version already has
      published binaries in the destination archive)
"""