Index: src/wp-includes/ms-settings.php
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--- src/wp-includes/ms-settings.php	(revision 27274)
+++ src/wp-includes/ms-settings.php	(working copy)
@@ -40,6 +40,7 @@ if ( !isset( $current_site ) || !isset( $current_blog ) ) {
 
 	$path = preg_replace( '|([a-z0-9-]+.php.*)|', '', $_SERVER['REQUEST_URI'] );
 	$path = str_replace ( '/wp-admin/', '/', $path );
+	$path = strtolower( $path );
 	$path = preg_replace( '|(/[a-z0-9-]+?/).*|', '$1', $path );
 
 	$current_site = wpmu_current_site();