Let me add to the original post. The same exact document, when opened on
another computer (also with Word 2003), does not exhibit these errors.

On the setup that is misbehaving, using TAB, SHIFT+TAB, or CTRL+TAB all
produce the exact same result inside of a numbered list. The position of the
text promotes to the next tab stop, but the outline level is unchanged.

Now I notice that in a plain line of text, SHIFT+TAB does not outdent, but
indents just as TAB. So I opened a blank document, and the same problems
occur. It is this instance of Word that isn't working right.

I've done everything I can think of to try and reset options and settings to
default, and no change. I am certain that the keyboard functions properly.

Thank you for any assistance.