'Add Menu' isn't working, Menus bug

Hi,

I’m not sure what is it. In my very simple template I have declared menu in functions.php:

add_action( 'after_setup_theme', 'register_my_menu' );
function register_my_menu() {
    register_nav_menu( 'primary', 'Header Menu' );
    register_nav_menu( 'secondary', 'Footer Menu' );
}

and in header.php:

<?php wp_nav_menu( array(
                'menu' => 'Main Nav',
                'theme_location' => 'primary',
                'menu_class' => 'nav-menu1'
            ));
            ?>

Menu is showing up no problem on site, but I can’t edit it from backend.
Adding new menus resulting in adding couple menus, which aren’t working at all, so isn’t deleting menus. I have no clue what’s going on.

I tried to reinstall wordpress, changing themes etc. but none of them helped.
Is this some king of bug?

Regards,
Pawel