Yup, I see your problem there, and I don't know how to fix it. You might be able to go back to the home page, recreate your search with fixed dates and still get the special pricing. But if that doesn't work out, you are going to be stuck calling the call center for help and paying the extra fee. You could also walk into the local ticketing office and explain the situation and see if they will waive the fee since it seems to be a website limitation.