1) Create a page with a table of contents at the top, then create content with various headings levels (e.g. h1, h2, h2, h3)
2) Save the page
3) Change the heading level of one of the lower level headings to a higher level one (e.g. h2 -> h1)
4) Preview the change and notice that the TOC does not reflect the change
5) Upon saving, the document TOC appears as expected