Hi Roscoe,
Without seeing your document, I can't really say with certainty why what you've reported occurred (and even then I might not be able to). I'm glad to hear you're using the Heading Styles but, again, without seeing your document it's hard to say whether the itemized lists are structured as well as they might be. You might find something useful in the articles here:
http://word.mvps.org/FAQs/Numbering/...gExplained.htm
and especially:
http://word.mvps.org/FAQs/Numbering/...eConflicts.htm
and:
http://word.mvps.org/FAQs/Numbering/...artMethods.htm