The promise that a certain version of Ubuntu will be supported for a specific number of mounths does not necessarily mean a promise to fix all bugs or even a promise to fix any bugs.
Note this quote from the Ubuntu web page for Desktop business users.
Stay up-to-date with free and regular updates and upgrades
See the graph called Ubuntu for Desktop Release Cycle. Notice that the next two LTS releases will get 2 years support for Hardware and Maintenance Updates and a further 3 year support for Maintenance Updates. That may include bug fixes but it does not imply a promise to fix all bugs during that period.
It is similar for the server LTS versions as this page for Ubuntu server business users shows. The main difference is that Hardware and Maintenance Updates extend for the full 5 year period.
As the link in your question to a bug report shows, it is often very difficult to determine exactly what package is causing the problem and we can also see that a lot of effort by volunteers is put into sorting out bug reports to determine which should have priority and who is responsible for fixing it.
When I read this page on helping with bugs I see that the Ubuntu development community is reacting to bug reports in a very orderly way.
You need to also consider that Ubuntu is a distribution. It takes software components from other parts of the Linux community and brings them together. What if the bug is in the Linux kernel, or Debian, or Gnome or some other component that Ubuntu does not have responsibility for.
The bug report has to be pushed to those responsible for maintaining and developing the package that has the bug. And it is then up to those people.
Sometimes the Ubuntu people can provide the fix as well as the bug report. It is important that the fix gets pushed upstream (as it is called) then all in the Linux community can benefit and not just us Ubuntu users. It takes time for the fix to go upstream, be accepted by those upstream maintainers, and come back downstream to be patched into Ubuntu.
I am not surprised that sometimes a decision is made to fix the problem in the next to be released version of Ubuntu rather than fix it in a version that is soon to be superseded. Especially if that next version is to be an LTS version with 5 year support.
You say that that particular bug is being fixed in Precise Pangolin but not in Oneiric Ocelot. But Precise Pangolin 12.04 has been under test for almost six months. By putting the fix into Precise, the fix gets tested.
This is better than putting it into Oneiric for users expecting a stable release to test it out, do you not think?
Fixing the past can wait. Get the future "precise" at the start. That is what is important, in my opinion.