Just throwing this out there as another potential idea (and I realize some will disagree with this).

Over the years I have simply abandoned using Word's numbering in numbered headings (although yes, using Styles helps greatly). I have preferred creating a style with the desired indentation and tab settings (but not a numbered style), and manually entering my numbers. Although that seems like a lot of work, I've been driven bonkers enough times by autonumbering that I found it the lesser of two evils. It's probably not practical for documents that might grow over time, but if you are working with a final draft, it's another way to go.