This can happen if you have background shading in the style and it is the full width of the page, you get the background behind the heading text and on the line above the page break. If that is the problem, it is a Word issue and you will get it in documents created in Word using the same styles.
I got around it by leaving the style as I wanted in the online help but reducing the shading in the Word template to being just behind the text.
If that is not it, then please add a screenshot.
See www.grainge.org for RoboHelp and Authoring tips
Thank you for the quick answer.
After investigating your reply (in Word forums) it certainly seams like it is related to a WORD and not ROBOHELP problem.
Sadly I cannot fix it in the way you suggest as the format for WORD documents is closely defined by my customer.
I will continue to search for the solution on WORD forums.