Page Listing not sorting correctly

Hi,

I have built a site that utilises a multiple item region. I use a perch custom call to return the list of items:

perch_content_custom('Articles', array(
   'template' => 'article-listing.html',
   'sort'=>'_id',
   'sort-order'=>'ASC',                     
));

This seems to work fine, i.e lists item 1, 2, 3,.....9, but as soon as the mulit-item region goes above item 10, the ordering gets lost, with the order becoming, 1, 10, 11, 12...., 2, 3, 4, 5, 6, 7, 8, 9.

I am presuming the 'default order' setting from with the 'Region Options' somehow overrides the setting from within the page.

Any ideas how I can get the order to be correct.

Did think about putting some sort of count on the item and then listing by this, but there must be more of a 'perch' way to go about this.

Thanks,

Andy