yes thats normal, the system simply carries over the original fx rate from the quote to the order. Are you subsequently changing the fx rate on the Sales Order? If you change it on the order the system will use the updated rate for the invoice and should not use the quote rate. There are two ways to overwrite it manually on the order:
1. change the posting date of the sales order. When the system retrieves an fx rate from your Currencies table it does this based on the posting date of your document or journal line, so changing the posting date will update the rate. When you change the posting date you will get a message asking if you would like to update the exchange rate, click yes.
2. in the sales order click the ellipsis by the Currency Code field
in here you can see what rate applies to your order and you can also change it
