[Amended] According to mysql.com this was a bug
It has recently been brought to attention that the MySQL man pages have been relicensed. The change was made rather silently going from MySQL 5.5.30 to MySQL 5.5.31. This affects all pages in the man/ directory of the source code.
You can tell the changes have come during this short timeframe (5.5.30->5.5.31). The old manual pages were released under the following license:
This documentation is free software; you can redistribute it and/or modify it only under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License.
The new man pages (following 5.5.31 and greater – still valid for 5.5.32) are released under the following license:
This software and related documentation are provided under a license agreement containing restrictions on use and disclosure and are protected by intellectual property laws. Except as expressly permitted in your license agreement or allowed by law, you may not use, copy, reproduce, translate, broadcast, modify, license, transmit, distribute, exhibit, perform, publish, or display any part, in any form, or by any means. Reverse engineering, disassembly, or decompilation of this software, unless required by law for interoperability, is prohibited.
This is clearly not very friendly of MySQL at Oracle.