We're currently working on trying to develop such an opensource tool that would allow bugs synchronisation between different bugtrackers. There's not much yet as the project just started a couple weeks ago, but I hope we can achieve something to solve that issue. Our first tasks have been to look at bts-link and also investigate the use of ontologies, RDF and semantic annotations or Linked Data concepts. More details here : https://picoforge.int-evry.fr/cgi-bin/twiki/view/Helios_wp3/Web/

There's also bugs-everywhere and similar tools attempting going distributed for bugtracking.

Debian has solved it using bts-link, which is an independent program from the bugtracker debbugs, FYI.

Well, actually, it's not exactly debbugs which handles that, but bts-link which explores remote bugs in distant (upstream) bugtrackers and notifies accordingly.

Would be very interested in talking to you, as we are doing the same thing, for one project of ours (Helios WP3)... will probably post another comment later to give more details.