If you are booking 180 plus 10, it will put a note up stating that you need a valid reservation number to book beyond the check in date. If you click the link it will ask for your reservation number and your check in date.
You're not going crazy, they've changed the system recently.
As mentioned above, now you will just pick the date and if it's more than 180 days out, you'll be prompted to confirm your resort reservation before you continue.