A family of Microsoft word processing software products for creating web, email, and print documents.
First of all, clear "Automatically update document styles" if it is selected.
If you are applying style sets to the document, note that these do not work reliably with numbered and bulleted styles. Avoid them and modify styles directly in the document instead.
Recreate the numbering for your headings as follows: Place the insertion point in the first Heading 1 paragraph of the document. Click Home tab | Multilevel List | Define New Multilevel List. Set up numbering as desired.
If you often create documents with heading numbering, set up a template with numbered styles.