Theme preview breaks HTML code in theme menu

[progmastery]

Theme preview modifies HTML code of navigation menu in some themes.

Here is an example:
​https://wordpress.org/themes/best-magazine/
​https://wp-themes.com/best-magazine/

This is how it should be
​http://themedemo.web-dorado.com/bestmagazine/

nav menu call parameters:

wp_nav_menu(	array(
'show_home' => true,
'theme_location'  => 'primary-menu',
'container'       => false,
'container_class' => '',
'container_id'    => '',
'menu_class'      => 'top-nav-list',
'menu_id'         => '',
'echo'            => false,
'fallback_cb'     => 'wp_page_menu',
'before'          => '',
'after'           => '',
'link_before'     => '',
'link_after'      => '',
'items_wrap'      => '<ul id="top-nav-list" class=" %2$s">%3$s</ul>',
'depth'           => 0,
'walker'          => ''
));

It seems there is some problem with wrapping menu, but I don't know if this is site issue or something related with WordPress version (ver=4.4-alpha-34443). Therefore I submitted this ticket here , not in w.org meta.

[hvianna]

Same problem here, with 4.4-alpha-34884

I verified the problem only occurs when you have 'container' => false in wp_nav_menu() and there's no menu assigned to that location (i.e., menu is generated automatically by WP). It then adds a blank tag (the container, that shouldn't be added) which breaks the layout.

Edit: I believe the problem is not related to theme preview (customizer), because it happens in the actual rendering of the site as well.

[obenland]

wp_page_menu() doesn't have the option to omit a container. 33974.diff​ will add a fallback.

[obenland]

In 34950:

Template: Add fallback for empty containers.

Since [14031] the container can be omitted in wp_nav_menu(). It can not
however in wp_page_menu(), which creates a conflict if it is set as
the fallback, Let's make sure there is always a valid container tag.

Fixes #33974.