Earlier in the year, we migrated the bugs from bugzilla.ubuntu.com over to Launchpad. This process involved changes to the bug numbers, since the Launchpad is used for more than just Ubuntu and already had a number of bugs reported in the system.
People often refer to other bugs in comments, which both Bugzilla and Launchpad conveniently turn into links. The changed bug numbers meant that the bug references in the comments ended up pointing to the wrong bugs. The bug import was done one bug at a time, so if bug A referred to bug B but bug B hadn’t been imported by the time we were importing bug A, then we wouldn’t know what bug number it should be referring to.
The solution we used was to just insert a link to the bug watch URL (e.g. https://launchpad.net/malone/bugtrackers/ubuntu-bugzilla/$BUGID), which allowed people to find the referenced bug, but was a bit ugly.
Today we ran a fixup script to remove these bug watch URLs from comments and rewrite the old Bugzilla bug numbers to the current Launchpad bug numbers. This cleans up the old imported bugs a bit so they fit in better with the bugs entered directly into Launchpad.