get_pages() not ordering as it should

I’m using get_pages() function to get all subpages from a page like this:

$childrens = get_pages(array('child_of' => 7, 
                             'sort_column' => 'post_date', 
                             'sort_order' => 'DESC', 
                             'depth' => -1));

This is supossed to get me a list of all pages (no matter if direct children, children of children, etc) orderen by the date they were created, but instead its showing me the list of pages in a strange order, here’s the output when I run a foreach on the $childrens array and output the post_date on each:

2011-05-10 15:37:03
2011-05-10 15:35:59
2011-05-10 15:01:18
2011-05-10 17:12:32
2011-05-10 15:00:47
2011-05-10 14:00:14
2011-05-11 04:19:08
2011-05-10 23:52:54
2011-05-10 15:20:12
2011-05-10 15:05:10

As you can see they’re not ordered by date descending, I tried using other options in the sort_column key but none seemed to e working correctly, does anyone know what could be wrong?

Thanks in advance!

This is indeed an error, and probably caused by the child_of argument.

Because child_of requests the whole subtree of the given page (not only the direct children, but also children of those children and so on), WordPress first queries for all the pages and then selects a subset of those pages. The first query respects the order, but the second subselection messes this up by just using array_merge().

I have created a Trac ticket for this.