100% correct, if the car is in your name the sticker should be your birth month no matter what, so the MTO messed up.
In my experience with 6 different cars and different times of the year the MTO has never given me a sticker for any month other than my birth month (which happens to be March). Even when i got a new car in November they gave me the option to get a sticker for March 2010 or a sticker for March 2009 at a discounted rate.