A family of Microsoft word processing software products for creating web, email, and print documents.
I've continued watching for answers to this issue, and the best answer I've seen so far is the following, from Allen Wyatt at wordribbon.tips.net:
"This problem has been reported by other Word users, as well. In all cases it seems that the problem is related to working with Word 2003 documents in a later version of Word. The problem is most likely rooted in how later versions of Word interpret and work with some obscure setting in the older Word 2003 file format."
http://wordribbon.tips.net/T009977\_Track\_Changes\_Thinks\_the\_Editor\_Has\_Changed.html
So it appears to be a bug in versions of Word after 2003, and there appears to be no prospect that Microsoft will fix it. After seeing this I began watching my Word versions closely, and it does appear to me that the problem arises only in documents that originated long ago in Word 2003.
The most reliable fix therefore is to re-create the document natively in our current version of Word. This is tricky, since just Saving As into the current version does not appear to solve the problem reliably. Nor does File | Info | Convert. And I'm not sure that copying and pasting the entire document into a new native current-version-Word document will necessarily solve the problem either, because copy-and-paste includes styles, and maybe other document metadata, and that might be exactly where the bug is hiding. We may have to copy and paste text only, removing all formatting, then re-do the formatting manually.
BTW, if you want to know whether your document will have this problem or not, there's an easy way to tell. Go to Review | Track Changes | Change Tracking Options and look at the checkboxes for "Moves" and "Formatting". If either of them is grayed out, then the problem will show up. If both are available, then *probably* this problem will not arise.