SVN policy

Hello, Apologies if this has been answered before, but after searching the various mailing lists I could not find an answer to this specific question. I recently reported bug: #49692. I had already found the bug reported in #47332 which was closed as 'bogus' and commented as 'Fixed'. So, I created another bug against the version I am using (5.3.0) as I assumed that the bug had made it back into this build somehow. A prompt reply was received telling me that the bug was indeed 'Fixed - in SVN' as per the initial bug reported against the 5.3.0beta1 version. The specifics of the actual bug are not so important. Now, my confusion lies around how a bug can be fixed against a beta version (5.3.0beta1) but yet is still resident in a later 'stable' release - 5.3.0 over 7 months later. I would have thought if this bug had been fixed against a prior beta version that it would have made up part of the stable release? Please can you enlighten me / point me at some docs outlining the release process / SVN policy for clarity. Much obliged, Rick Walker.