Word 2000: SHIFT+TAB does not decrease indent

[Liam]

In other applications on my XP Pro SP1 machine, SHIFT+TAB decreases the
tab indentation, as expected. Insertion pointer hops one tab to the
left. So the keyboard appears to be working. However, on Word 2000,
SHIFT+Tab tabs to the right. This is the behavior regardless of whether
I check or uncheck Tools-Options->Edit "Tabs and backspace set left indent".

If anyone encountered this problem and knows how to fix it, I'd be
grateful for the tip.

Thanks
Liam