This is an excerpt from a control ACK message I received recently:
Processing commands for control@bugs.debian.org:
[...]
--
600231: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=600231
598496: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=598496
-1: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=-1
As you can see, the negative "new ID" is included in the list of URLs in the
footer.
Attached is a bit of a guess at a patch, not tested (I've not got round to
setting up a local debbugs to play with!).