Index: wp-admin/includes/class-wp-posts-list-table.php
===================================================================
--- wp-admin/includes/class-wp-posts-list-table.php	(revision 35609)
+++ wp-admin/includes/class-wp-posts-list-table.php	(working copy)
@@ -137,7 +137,11 @@
 	 * @return string The value of 'orderby'.
 	 */
 	protected function get_orderby() {
-		return strtolower( get_query_var( 'orderby' ) );
+		if ( isset( $_GET['orderby'] ) ) {
+			return $_GET['orderby'];
+		}
+
+		return '';
 	}
 
 	/**
@@ -149,7 +153,11 @@
 	 * @return string The value of 'order'.
 	 */
 	protected function get_order() {
-		return strtolower( get_query_var( 'order' ) );
+		if ( isset( $_GET['order'] ) && 'desc' === $_GET['order'] ) {
+			return 'desc';
+		}
+
+		return 'asc';
 	}
 
 	/**