I've always been curious...why when I'm reading an HTML formatted email (say Woody's Windows Watch), does the text seem to jump back to a previous location if I open another window and come back.

For example. I'll be in the middle of a long section, switch over to Word to type another paragraph of a long report then switch back to the open email to continue reading but now the text jumps back to the start of the section instead of staying where I was reading. What causes this?