OK, I understand the thinking behind the jump now though I do not agree with it.
It jumps when the state/province/country is changed (not because the tick box is ticked) and it jumps to the top so the shopper can see the new shipping cost which is no different if the delivery details are the same.
A better way to do it and the way other carts do including mals-e is to allow the shopper to select a shipping option at the View cart stage. The option is then saved in cache
The shopper can then change their shipping option at checkout if they want to.
This way, the shopper can see the shipping cost change as they buy more as well as change their selected shipping method at checkout
Shipping cost is very important to online shoppers. Nothing like arriving at checkout to see shipping is way over the top