Category required not working

@Miller
In item-post.php find this code:
<input type="hidden" id="catId" name="catId" value="<?php echo osc_item_category_id(); ?>"/>
and replace it with:
<input type="hidden" id="catId" name="catId" value="<?php echo $prepare['i_category']; ?>"/>

Now only main category required
Subcategories not

Because osclass does not differentiate what is category and subcategory on publish page, you have only 1 input.