Why there is not bug fix in GA version
By Sveta Smirnova-Oracle on Jun 02, 2009
Reporter of bug #44604 pointed to common problem: "Why don't backport bugfix to previous major version?" Especially if this version is GA.
This particular bug seems to be fixed by redesign of MySQL Optimizer which was dramatically improved in version 6.0
At the same time while some feature is improved in new version backport this improvement or even part of it into older one is not easy and can lead to instability or affect other applications. There is always balance between risk and effort to fix.
Same reasons apply for other bugs in similar state.
Of course this applies only to bugs with good workaround or to rare cases and should never apply to crashing bugs. While sometime is not easy to properly fix crashing bug in stable version. Example of such a bug were bug #37846 and bug #37847 Real fix for version 5.0 contained message in error log instead of crash while in 5.1 error doesn't occur at all.