I had an identical experience to the OP's last week whilst trying to book one-way MCO-PHX. Sat on hold for 36 minutes waiting for a CSR at their call center; once reached, booked without any issues or delay, and at the website fare. The CSR was good enough to waive the $10 call fee (though she did neglect to include the $25 fee for a carry-on; I ended up having to pay that at check-in). Why the problem occurred, I have no idea; there does seem to be a problem with their website when one is trying to book a one-way, though.