Steps to reproduce the issue

The main menu become corrupted since version 3.6.4, and probably after changing the order of submenu items.

Expected result

See the website in the Arduino main menu http://www.avdweb.nl/

Actual result

Suddenly there arised double submenu items in the arduino main menu , thus the old correct submenu item in submenus, and the double spooky submenu items in the parent menus.
In the administrator menu editor:
1 selecting and editting the old submenu item in the submenu is ok
2 selecting the double submenu item in the mainmenu result in the error
0 Error decoding JSON data: Syntax error

System information (as much as possible)

PHP Built On Linux linux91.webawere.nl 2.6.32-673.8.1.lve1.4.3.1.el6.x86_64 #1 SMP Thu May 5 16:06:47 EDT 2016 x86_64
Database Version 5.6.29
Database Collation latin1_swedish_ci
Database Connection Collation utf8mb4_general_ci
PHP Version 5.3.29
Web Server Apache/2
WebServer to PHP Interface litespeed
Joomla! Version Joomla! 3.6.4 Stable [ Noether ] 21-October-2016 16:33 GMT
Joomla! Platform Version Joomla Platform 13.1.0 Stable [ Curiosity ] 24-Apr-2013 00:00 GMT
User Agent Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.99 Safari/537.36

Additional comments