Items included in Navigation - Headings that shouldn't be

The Navigation pane includes any paragraph whose "Outline level" (in the Paragraph dialog box) is different from "Body Text."

Since the documents were created in older versions of Word, the culprit here is most likely the Document Map (= the predecessor of the Navigation pane) which was buggy in the sense that it tried to guess which paragraphs were intended to be headings and therefore applied an "Outline level" more or less at random to these paragraphs. Captions and other short paragraphs were often affected.

You can fix the problem by running the macro in the article at http://word.mvps.org/faqs/general/DocumentMap.htm.

Yes, you can modify this behavior. For each style that you want left out of the Navigation Pane, follow these steps:

1. Press Alt + Ctrl + Shift + S to open the Styles list.
2. Select a style you want to eliminate for the Navigation Pane.
3. At the right end of the style name, click on the down-pointing arrowhead and choose Modify...
4. In the bottom left corner of the next dialog, click on the Format button and choose Paragraph.
5. Change the Outline level to Body Text. OK Out.

Please note, you can't change the outline level of built-in styles like Heading 1.