I have a plugin that inserts a tinymce like shown below. Something causes the second toolbar, the theme_advanced_buttons2 to have display:none attached to their style attribute, effectively hiding them.

I don’t manage to find the code responsible for this.

$tinymce =  

array
(
      'theme_advanced_buttons1' =>

         '                       \
            ,  undo              \
            ,  redo              \

               ...
               ...

            ,  indent            \
         '

   ,  'theme_advanced_buttons2' =>

         '                       \
               link              \
            ,  unlink            \

               ...
               ...

            ,  help              \
         '
);

wp_editor
(
      $text
   ,  $editor[ 'name' ]
   ,  array
      (
           'tinymce'   => $tinymce
         , 'quicktags' => $enabled
      )
);

I found the right answer here thanks to a comment by mrwweb:

Show the Kitchen Sink by Default

If you would like to show that second row of options by default, there’s an easy way. Simply put the following into your theme’s functions.php file (Appearance > Edit > Theme Functions – functions.php):

function unhide_kitchensink( $args )
{
   $args['wordpress_adv_hidden'] = false;
   return $args;
}

add_filter( 'tiny_mce_before_init', 'unhide_kitchensink' );

Show the Kitchen Sink by Default

^{Copying @nus’ answer as an answer to help newcomers.}

If you would like to show that second row of options by default, there’s an easy way. Simply put the following into your theme’s functions.php file:

function unhide_kitchensink( $args )
{
   $args['wordpress_adv_hidden'] = false;
   return $args;
}

add_filter( 'tiny_mce_before_init', 'unhide_kitchensink' );