Has anyone run into this?

I'm 5 star member & rented a full size 4door at Houston Hobby. Plenty of prem. class (and all other class) cars on lot but they refused to upgrade without paying. They said that because the car they had given me had a sunroof it was an upgrade - since sunroofs are non-reservable.

To me thats like saying that – It's hot in Houston. Since colors are non-reservable and white cars reflect heat a bit better than dark cars, a white car is an upgrade.

Does anyone here consider a Taurus with a sunroof a car class upgrade from a Taurus without a sunroof? Did I mis-read the 5 star program - is it any upgrade and not a car class upgrade?