Originally Posted by Charles Kenyon

Are you sure that the font-size in the original text is set in the style and not through direct formatting?

BTW, keeping automatically update styles from template checked is the source of problems when documents are sent to a different computer. What happens when I send my document to someone else? Will Word mess up my formatting?

I'm not sure why you are breaking your chapters into separate files. Word will handle much larger documents than 200 pages. The largest I've put together was 10,000 pages +. You do want to use heading styles and the navigation pane to navigate a larger document.