Bug in total for tiered pricing

qty 1 and 2 shoudl be 20 and 40 respectively, but if you go to qty 3 or more and then back to qty 2 or 1 , the total price is wrong, even though the woocommerce price per unit is correct.
See video to see it in action:
https://youtu.be/MyHYhRr-0qE