I’m not sure when this problem was introduced, but it still exists in Graphene 1.5.2.
The problem exists on my test server which is running MySQL 5.5.9 as well as my ISP on MySQL 4.1.22
If I change the line in loop-children.php from
‘orderby’ => ‘menu_order, title’,
to
‘orderby’ => ‘menu_order , title’,
the child page excerpts appear as expected when the parent page has no content.
In other words, there needs to be a space before the comma.
Can you roll this change into the next update to Graphene?