This has now been solved:
You have to make some changes to the search form template:
I made a duplicate of the file \modules\mod_cck_search\tmpl\default.php and called it override.php
The Seblod search form uses these fields
Search for:
<input type="hidden" name="search" value="<?php echo $preconfig['search']; ?>" />
<input type="hidden" name="task" value="search" />
Replace the lines with:
<input type="hidden" value="com_cck" name="option">
<input type="hidden" value="list" name="view">
<input type="hidden" value="<?php echo $params->get( 'menu_item', '' ); ?>" name="Itemid">
<input type="hidden" value="<?php echo $preconfig['search']; ?>" name="search">
<input type="hidden" value="search" name="task">
In the SEARCH MODULE settings, go and change the template in advanced to your new template file.
Thanks to Cyril who posted the solution