here is the reply of kunena...
http://www.kunena.org/forum/K-2-0-General-Questions/125171-kunena-menu-conflict-with-mainmenu-template#134099I can understand your assumption, but if you study the way that Joomla and Kunena code is processed on your or any site you will see that the problem can only be caused by the reverse of your suggestion.
Your main menu template is in conflict with the Kunena menu.
There is code in your custom Joomla template that is making it incompatible with Kunena.
The only people that would be able to fix this are those that wrote your Joomla template.