TinyMCE: show menu with block formats in additional editor instance

I'm running multiple instances of tinyMCE.

Problem: I want to use the select menu with block format options (h3, h4 
...) but it doesn't show up. Is there anything more to add except 
"theme_advanced_blockformats : "h3,h4"?

Everything works fine, if I'm using the standard editor instance.

This is my additional configuration:

tinyMCE.init({
mode : "textareas",
editor_selector : "MyEditorConfig",
content_css : "http://bla/blu/tinymce.css",
width : "500",
height : "400",
browsers : "msie,gecko",
inline_styles : "true",
apply_source_formatting: "true",
remove_linebreaks: "true",
theme : "advanced",
theme_advanced_toolbar_location: "top",
theme_advanced_statusbar_location: "bottom",
theme_advanced_resizing : "true",
theme_advanced_resize_horizontal : "true",
theme_advanced_blockformats : "h3,h4",
theme_advanced_buttons1 : 
"italic,bold,bullist,numlist,undo,redo,link,unlink",
theme_advanced_buttons2 : "styleselect,cut,copy,pastetext,nonbreaking",
theme_advanced_buttons3 : "",
extended_valid_elements : 
"span[*],p[*],code,pre,blockquote/quote,a[*],img[*]",
entity_encoding : "raw"
});

Can anybody help?

Cheers
Karsten