When I level up, hit point buttons change all dice

[pcg79]

When I level up and hit either the "Random" or "Average" button to calculate my new HP it changes the hit point dice for all the levels up to that point. It seems like the correct behavior would be to only change the latest unset die.

From the Player's Handbook:

Each time you gain a level, you gain 1 additional Hit Die. Roll that Hit Die, add your Constitution modifier to the roll, and add the total to your hit point maximum.