Index: wp-includes/ms-blogs.php
===================================================================
--- wp-includes/ms-blogs.php	(revision 25706)
+++ wp-includes/ms-blogs.php	(working copy)
@@ -274,6 +274,10 @@
 	foreach ( array_intersect( array_keys( $details ), $fields ) as $field )
 		$update_details[$field] = $details[$field];
 
+	// Ensure that path has a trailing slash and prefixing slash
+	$update_details[ 'path' ] = sanitize_title( $update_details[ 'path' ] );
+	$update_details[ 'path' ] = "/{$update_details[ 'path' ]}/";
+
 	$result = $wpdb->update( $wpdb->blogs, $update_details, array('blog_id' => $blog_id) );
 
 	if ( false === $result )