The Ultimate Debian Database helps show ubuntu/debian package relationships.
http://udd.debian.org/
http://wiki.debian.org/UltimateDebianDatabase
Unfortunately Debian and Ubuntu use incompatible bts systems. Currently Ubuntu's launchpad based bug tracking system _bts_ is lacking accessible package version information. Bug tracking information tied to package version is essential for debian where packages go through many version iterations between releases. Package bugs should not be tracked based on the release. They must be tracked based on their version.
This was part of the original design for Launchpad Bugs, but it never
came to fruition. The very earliest bug still open on Launchpad Bugs
asks for this:
https://bugs.launchpad.net/malone/+bug/424
Up to and including Hardy, ubuntu used apt-listbugs which referred to
debian's bts with package version tracking. Even though this pulled bug
information from the debian bts, it gave a reasonable indication of
what packages contained significant bugs. apt-listbugs was withdrawn,
because ubuntu package customization increasing has made the related
debian bts irrelevant.
Topic branches and topic trees of are ways by which package customization can be tracked.