I wrote a mini-survey of distributed bug tracking in 2008 here:
http://travisbrown.ca/blog.html#TooMuchAboutDistributedBugTr...
But don't dismiss them.
Fossil, which is not strictly a distributed tracker but rather an entire source-control system, is still maintained and very active. Several popular projects use it. And you do get distributed issue tracking for free.
BE is actually pretty mature. Development has stalled, but you have an email and web interface along with a pretty extensive bug manager which is certainly more advanced than Github issues. When configured with git, it's easy to chose where bug storage should be in-branch or use a dedicated branch.
Using the VCS itself to store data has its advantages. As the early proliferation of projects showed, implementing a distributed bug tracker on top of a distributed VCS is almost trivial. The truth is that if github added support to embed issues in BE format under a dedicated branch, BE would become massively popular.
Then you also have SimpleDefects (SD), which actually implements his own distributed database, web interface (which I'm using) and a bi-directional syncronization plugin system. Way harder to implement, and it's not surprising that SD is less mantained than BE, even though it would hold much more promise (a github issues sync plugin exists, but has bitrotted).
SD, in its current state, is also more featured than github issues.
Give these projects a spin. Contributing to BugsEverywhere in particular is not hard.
My big question is why distributed bug trackers aren't more popular considering the popularity of distributed version control and the general weakness of the bug trackers on sites like github or bitbucket.