Word 2007 changes "Outline Level" to Level 1 randomly to paragraphs

I experienced this recently when I was busy finalizing some documents. How to prevent/fix this annoying Word 2007 behavior as follows:

Tips to prevent or deal with the problem

• Exclude the TOC until you’re ready to either print the document or convert to PDF. The TOC and the DM seem to interact to create instability.
• Always close the DM pane before closing your file or Word. The DM is more stable when a document is opened with the DM pane is closed.
• Always open documents with DM pane closed. If you’re uncertain, start Word first, close the pane, then open your document.
• You can tell that your DM is being scrambled if Word shows the “Word is formatting the document…” status bar while the file is opening.
• Always check your DM when you first open the file.
• The only time I’ve noticed a DM become scrambled is on open. This doesn’t mean there aren’t other times it’ll become scrambled. For example, I’d be cautious by closing the DM pane when generating a TOC, or printing or converting documents to PDF, especially if they contain a TOC.
• I don’t know what makes a file susceptible to scrambling on open in the first place.
• As soon as you notice your DM is scrambled, close your document without saving.
• Saving the file with a scrambled DM will permanently scramble both the DM and the TOC. It’s actually the heading level tags that get scrambled.
• Use Word’s auto-backup feature: Tools -> Options; Save tab; check “Always create backup copy.” Lets you roll back one save.
• Create and keep frequent backups of your own, even several in a day if you’re being particularly productive: time is precious; disk space is cheap.
• If you don’t need the really rapid navigation offered by the DM, try using Outline view instead. According to what I’ve read, it’s not prone to scrambling.
• Additional observations: Merging an older, unscrambled copy with a scrambled copy passes the scrambling on to the good copy, no matter which direction you merge (good into bad, or bad into good), or which document’s formatting you opt to retain. I haven’t found any way to repair/recover a scrambled and saved file, but I haven’t tried any commercial recovery products.

To remedy
If your DM becomes scrambled and you haven’t saved your document:

1. Close the document and Word without saving
2. Open Word
3. Close the DM pane
4. Open your file

From another comment by by Jan Zambor :
To repair a scrambled doc:
1. select entire doc (Ctrl+A)
2. go to Paragraph windows
3. set Outline level to "Body Text" (headings will NOT be set to body text, you should end up with the correct doc)