in bug_graph_bystatus.php change the call:

graph_bydate( $t_metrics, $t_labels, lang_get( 'by_category' ), $f_width, $f_width * $t_ar );

to:

graph_bydate( $t_metrics, $t_labels, lang_get( 'by_status' ), $f_width, $f_width * $t_ar );