How does Ubuntu support work
Solution 1:
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made to fix the problem in the next to be released version of Ubuntu rather than fix it in a version that is soon to be superseded.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.
Solution 2:
For example current Oneiric will be supported till April 2013. What does that mean and what happens by that time?
It mainly means that technical support concerning Oneiric version will be provided until its end of life, that is April 2013. You can also be sure that critical and security bugs affecting Oneiric will be fixed until April 2013.
If a bug is found in one of Ubuntu supported packages - will it be fixed?
Depending on the severity of the bugs and the packages affected by the bug, it may or may not be fixed.
Solution 3:
There is no guaranty that if a bug is found it will be fixed. Period. Even on the current or development version. Some bugs are fixed, some not, it depends on available resources, bug severity, etc...
What is sure if that a bug is fixed, and it is a security or critical one, it will be back-ported to all supported versions. Also, in some supported versions, you will receive updates to some selected packages (like firefox) until its end-of-live.
The most important thing about support, from a normal user point of view, is that the repositories of any versions will remain online only as long as it is supported. If you are using an unsupported Ubuntu version you won't be able to install or update software using the normal means (apt-get with official repositories, Software Center, etc...).