Why aren't styles updating?

[Tunathedog]

I just tried to set all Normal paragraphs to have double-spacing. So did a Modify Style. But the Normal paragraphs didn't change. They only change if I select them and set them (again) to Normal. I've noticed this kind of thing several times before. How do you tell Word to make style changes override any special formatting in a paragraph? (OK that's maybe two question, but they're closely related.)