Hi,
Are you sure that you're using the latest build ?
And do you have some overrides for the back product views ?
Because the code which generate the SQL is
$query .= ' ELSE ordering END WHERE variant_characteristic_id IN ('.implode(',', $product->characteristics).') AND variant_product_id = '.(int)$status;
But that code is in a block
if(hikashop_acl('product/edit/characteristics') && !empty($product->characteristics)) {
So it means that your variable is in the same time, not empty (because it enter into the "if") and empty (because the result of the implode is an empty string).
I have to admit that I don't understand.
Regards,