When a Sell-to Address is updated on a Sales Order (or invoice) there is a prompt to ask if you want to update the Customer, if you say yes the Customer is updated, the Ship-to Address is also updated (if Ship-to is set to Default) but not the Bill-to Address on the Sales Order. This then means when you invoice the order the address at the top is incorrect, plus it adds a Ship-to Address at the bottom (with the incorrect address on it).

The Bill-to Address should be updated at the same time (if the Bill-to Customer is the same).

There is also no way of manually changing the Bill-to Address unless the Bill-to Customer is changed (at which point for some reason the address becomes editable) this means there is no way of updating address details on a cash non-account Sales Order.