Sorting in columns

I am using the page-list-cols code – but it seems to sort the pages by column, rather than by row.

For example, it displays as:

A D G
B E H
C F I

Rather than as:

A B C
D E F
G H I

Is there any way of changing this?

Here’s the shortcode I’m using: [pagelist_ext child_of="997" show_content="0" sort_order="asc" class="page-list-cols-3" image_width="300"]