You quote version 3.23, yet talk about subqueries which didn't get added until version 4.1.

ONLY_FULL_GROUP_BY was added in 4.0 but only applied to select list columns, the 5.0.23 mentioned above applies to the HAVING clause list not allowing them as well:

http://dev.mysql.com/doc/refman/4.1/en/server-sql-mode.html#...