Scrolling in Word duplicates headings

[Info. Sys.]

When scrolling through a Word (XP) document using the
mouse wheel, the headings (using style-heading1 or 2)are
duplicated and can even be edited. To make the duplicate
disappear, I have to scroll or page down to another
section of the document, then go back and the duplicate
is gone. Something like this:

before: Heading1
after scrolling: Heading1
Heading1

Any ideas?