Re-indexing without re-installing

The help centre article on Google Desktop
<http://desktop.google.com/support/bin/answer.py?answer=12899> says you
have to uninstall and reinstall Google Desktop in order to force
re-indexing. On the other hand, there's also the TweakGDS plug-in
http://desktop.google.com/plugins/i/tweakgds.html which you can install
to perform re-indexing.

But this morning when I logged in to my Windows account, Google Desktop
initiated first-time indexing on its own. I checked the GDS version,
and it's still the same one (20051111-en) so it couldn't have been
caused by an upgrade. Does anybody know what has caused the
re-indexing, and more importantly, can I trigger it manually?