If you are using Word's built-in heading styles to create your outline, the
problem is that Headings 1-4 are by default formatted as "Keep with next."
This is desirable for headings but not for a corresponding number of levels
in an outline. Go to Format | Paragraph | Line and Page Breaks and remove
this formatting from paragraphs in, say, Headings 3 and 4, then update those
styles.