WTF Happened to ActionMailer?

For the record, I'm upgrading from 2.0.2

ActionMailer works great on 2.0.2.

I have a thank you email that I want sent as multipart mime so I have

thanks.text.plain.erb
and
thanks.text.html.erb

Then in my ActionMailer::Base subclass I have

def thanks(order)
        recipients order.emailAddress
        from "Us <do-not-reply@ourwebsite.com>"
        headers "Reply-to" => "do-not-reply@ourwebsite.com"
        subject "Thanks for your order"
        sent_on Time.now
        tickets = order.purchaseTransaction.tickets
        body :first_name => order.nameFirst,:quantity =>
tickets.size, :amount => "$#
{order.purchaseTransaction.payment.amount.to_money}", :order_number =>
order.id, :ticket_date => tickets.first.validForDate, :order => order
  end

I get a single email message with a mime type of text/plain and the
contents actually created from the thanks.text.html.erb. Looks like
crap. Why in the world was this lovely bit of solid bullet proof
functionality messed with at all and how do I get it working again?