First time it happened, I couldn't believe. I thought it was I who screwed up that document: I wondered what I could have done to the document styles to get those spurious entries into the table of contents. Then it happened again. And again. It couldn't be me, simply.
I'm working at a client which is committed to produce its documents with Microsoft Office 2007. No way to change that: I had to purchase a license and install it onto my virtualized Windows. When I'm at work, I just use the client's computers. When I'm at home, I run Windows on a Solaris host with Sun xVM VirtualBox to get the job done.
A few days ago, just before sending to print the last revision of a document, I realized that the table of contents was screwed up! Instead of just listing heading up to level 3, it was showing spurious lines here and there. Some of them, were image captions, too. The first I tried to correct the problem was selecting the guilty lines, checking the paragraph options, which incidentally seemed ok, and reapply the original style. It worked, but everytime I opened the document, the table of contents was screwed up again. I tried to understand what happened, given that the spurious lines weren't that spurious (they were always the same), but found nothing. I google a couple of minutes just to confirm I wasn't alone.
I later discovered how I could reproduce the problem: it always happened when I closed the guilty document with the document map feauture on. Switching off the document map solved the problem and the next time I opened it it was just fine.
I recognize that's not a great solution but hey, it works.