I’m running the JA Nex 2.5 template on a Joomal 2.5.4 site (see http://therebel.org/.) After installing K2, suddenly the extended menus are no longer working. The main menu points are showing but the sub menu options are not. When I disabled the K2 extensions in the extensions mangager, the extended menus started working again. Turning them back on, one by one, returned the result that the one and only K2 extension conflicting with the mega menu is the K2 System extension. I checked in the extensions manager and there are no settings in the K2 System plugin that I could change to make the extended mega menu properly display the submenu points.