Comment 11 for bug 507603

debbugs bug syncing isn't handled by simple HTTP fetches; it works by rsyncing the bug database and parsing it directly, so it's much more involved than just providing a valid URL. At the moment the code in lib/lp/bugs/externalbugtracker/debbugs.py is hardcoded to deal with just one such rsynced database; any work on fixing this bug would need to start by adding support for an rsynced database per tracker.

Alternatively, it might be worth exploring whether the SOAP interface that IIRC debbugs has these days could be used instead of the rsynced mirror. I don't know whether the instance on gnu.org supports this, though.