disable features introduced after Word 97 set automatically on Sav

Here's a problem I cannot sort out.

I find that when I save some files the "disable features introduced after
Word 97" Option (on the Save tab) is automatically set, even if I explicitly
disable it just prior to the save. One of the really irritating things is
that it is unpredictable and erratic.

I have made sure that all of the templates I use, including normal.dot, have
this option disabled.

What, either in the document itself or in the environment, would cause this
behaviour?

Rick