That's because you're using a DATE field, and those update regardless of the "update automatically" setting. Instead of using a DATE field, you might consider a:
• CREATEDATE field, which updates only when the document is first created or is subsequently saved via Save As;
• PRINTDATE field, which updates only when the document is printed; or
• SAVEDATE field, which updates only when the document is saved.
Alternatively, you could lock the problem field or convert it to text.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]