I see, so it's a "Brit" thing. I understand that we each have different ways of spelling things but you would think in the end what is in the dictionary should win out over cultural barriers.
There probably are some words that can be spelled, and acknowledged by the dictionary, using either word. But not all.
Jumper is a new one for me too. When I was a kid my Mom wore a frock on the weekends around the house that she called a "jumper", but it wasn't even remotely close to a sweater. It was more like a house dress.