> If you reload the page in your browser after you modify the zone to StateB, do the taxes now show up properly?
Simple reload just clears all the user data and starts with no taxes, as well as no entry in the address at all, so it is not really a useful step. "Review Order" however does clear the old tax and so just the new tax.

However, the expected behavior is that when you change the zone (state), the old tax should go away and the new tax should appear.

Indeed same problem. I am moving my discussion to that thread.