Answer: When Oracle acknowledges the bug in 5.5.25 (to the owner only), corrects the bug in 5.5.27 (to the owner only), yet hides all information of its existence.
Recently a colleague and good friend discovered a bug in MySQL 5.5 replication that would crash MySQL. This was initially reported as Bug #65740, and after a lot of back and forth, a reproducible test case was found. Excellent work on the part of my colleague to spend the time to clearly identify the specific conditions. I remember looking at this initial thread in detail for an UPDATE statement using variables combined with an –ignore-database configuration option.
For no explanation by Oracle, this bug was subsequently marked as private (after I originally viewed the thread publicly), corrected, and the corrected bug is not referenced in the 5.5.27 Release Notes, yet the private bug clearly states.
[20 Jul 11:59] XXXX Fixed in 5.1.65/5.5.27.
The reason why I raise this concern is due to the lack of consistency. Why this was not included in the Release Notes is not acceptable in my view. However, the installation of 5.2.25 was needed to address another obscure Bug #45670 that was corrected and remains open to the MySQL Community.
I do not know of [yet] a public statement by Oracle that details why certain information about MySQL is open, and certain information is closed.