Some users are finding that the font of the entire word document
changes from either Times or Arial to Symbol with no prompting. Most
commonly this happens when the user saves the document, though it has
been reported that it happens during typing. There is no consistent
trigger that we know of and the problem is intermittent - happens once
a week or so.

The text can be highlighted and then changed to a different font e.g.
if first font was Times, then changes to Symbol, font can be changed to
Arial but not to Times (which shows as symbol).

Times can be used succesfully in another document.

Any ideas why this might be happening and suggestions on resolving the
issue?