Words starting with accent are not sorted alphabetically using auto-nav

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Hi,

I'm having a trouble with sorting auto-nav alphabetically in case that first letter of word has an accent. For example: "ě,š,č,ř,ž,ý,á,í,é". For some reason, it works well only using page-list. But i need to use auto-nav.

Check out the website:
Auto-nav is used in the left sidebar (word "čerstvé těstoviny" has to be right after words starting with a, but its in the end):
http://blobmedia.cz/test/administrace/index.php/nabidka/cerstve-tes...
But pagelist works fine:http://blobmedia.cz/test/administrace/nabidka/...

This code i use for displaying the autonav:
<?php 
   $page = Page::getCurrentPage();
   $bt_main = BlockType::getByHandle('autonav'); 
   $bt_main->controller->displayPages = 'custom'; // top, above, below, second_level, third_level, custom (Specify the displayPagesCID below)
   $bt_main->controller->displayPagesCID = $page->getCollectionParentID(); // <-- Specify the CID of the page named: REPERTOIRE ( Gets the first level of pages under that section )
   $bt_main->controller->orderBy = 'alpha_asc'; 
   $bt_main->controller->displaySubPages = 'none';  // none,  relevant, relevant_breadcrumb, all
   $bt_main->controller->displaySubPageLevels = 'none'; //custom, none
   $bt_main->controller->displaySubPageLevelsNum = '1'; // Specify how deep level 
   $bt_main->render('view'); // Specify your template or type "view" to use default
?>


I just need to expand this sorting ability with some extra characters somehow. Maybe somewhere in MySQL? Any ideas?

I will appreciate any suggestions.
Thanks!
David