based on wordpress' template hierarchy, index.php is sought only when there's no alternative. i used wordpress 2.7 from the svn.
when i goto somewhere.com/?m=200808
with a child theme applied,
wordpress 2.7 will choose to display it with the index.php of the parent theme. i expected it to use the child theme's because on "home" (is_home) is does us the child's index.php