Meta Box

I meant that I can do this as a bug report 🙂 not a feature request. Sorry if I wasn't clear enough :). The metabox is displayed on options page:

https://ghostbin.com/paste/7wb5y

Updated the plugin and the extension and I still can do this. But only the outer group can be moved to inside group. The nested group is fine.

Yes but it seams to only work with separate fields (not whole groups) and you still can remove or add more copies.

I work currently on windows 10 with XAMPP installed, PHP version 7.1.6. WordPress 4.8.

Everything is basically copied from docs. Metabox and extensions are included directly in my plugin files. Metabox 4.12.2 and MB Settings Page 1.3

(I don't know how to format code because the editor here has no buttons)

the field:

    $meta_boxes[] = array(
        'id'         => 'brt-header-scripts',
        'title'      => __( 'Scripts before </head> tag', 'brt' ),
        'settings_pages' => 'brt-scripts',
        'fields' => array(
            array(
                'id'   => 'brt-head-scripts',
                'type' => 'textarea',
                'clone' => true,
                'sort_clone' => true,
                'add_button' => __('Add another', 'brt'),
                'attributes' => array(
                    'style'  => 'height:250px',
                ),
            )
        )
    );

the setting page:

    $settings_pages[] = array(
        'id'          => 'brt-scripts',
        'menu_title'  => __( 'Additional scripts', 'brt' ),
        'parent'      => 'brt-options', 
    );

Ok, I think this code fixed the issue:

function filter_html_options( $new_value, $old_value ) {
    array_walk_recursive($new_value, function(&$value) {
        $value = stripslashes ($value);
    }); 
    return $new_value;
}

function plugin_init() {
    add_filter( 'pre_update_option', 'filter_html_options', 10, 2 );
}
add_action( 'init', 'plugin_init' );