Hi Guys;
I’ve had the same issue – I found the quickest and easiest fix was to replace the following core files from previous version (3.9.2).
Files found in /wp-includes/
– nav-menu-template.php
– nav-menu.php
Might not be the BEST fix, but definately fixed it for me (it was the only issue that I had with my theme).
Hope it helps someone out there.
Peace.