Version 1.5.5
Line 755
change
$category_base . '/' . strtolower( The_Events_Calendar::CATEGORYNAME ) . '/month' => 'index.php?cat=' . $categoryId . '&eventDisplay=month',
to
$category_base . '/' . strtolower( The_Events_Calendar::CATEGORYNAME ) . '/month' => 'index.php?cat=' . $categoryId . '&eventDisplay=month' . '&eventDate=' . date('Y-m'),
