This is not what happened to me in March 2013. I was in a category 8 and wanted to upgrade to a T. I was quoted a rate $7,000 more than the original rate was for T concierge when I booked.
These are the responses that I got from
DCL
"Whether it be a
Travel Agent, Guest, or an Agent at
Disney Cruise Line,
when a category is changed on a reservation it is always at the
prevailing rate. This has always been the way our reservation system
works. The reservation system (availability and pricing) is the same
whether you call us or go online at
www.disneycruise.com.
With that being said, it could be that when the category change is being
made the price is still the same as when originally reserved. However,
we always tell our Guests pricing and availability is subject to change
without notice. It is possible to reserve or price a cruise in the
morning and call back later that day and the cost be higher."
" Please allow me to explain, when stateroom categories are waitlisted it
means that staterooms in the category you are requesting are not
available and therefore pricing for the staterooms is also not
available.
The reservation is booked at the prevailing rate, since all pricing and
availability are subject to change until a reservation has been booked."
"For example, if you reserve a cruise in March, 2013, and are given
prices for different categories, those prices are valid for that point
in time. If you reserve that cruise for a particular category and
receive a confirmation number, that is the only category that has the
price 'locked-in'. If you contact us a few months later and choose to
change the stateroom category, you will be provided the price of the
category on that date, not the date in March, 2013, when you originally
booked the cruise.
That is the reason we encourage our Guests to select the stateroom
desired (if possible) at the time of reserving the cruise since pricing
does change and in most cases will increase as the saildate gets closer."
So basically my understanding is, if the category you want to upgrade to was sold out, once it becomes available you will be paying the current rate.