IE does this, it is a default behavior, it acts like a form reset button, much the same way that hitting Return does a form submit.

It does not seem to be a very likely thing for a user to do by accident. There are a TON of hotkeys which can affect your browser, you can not stop all of them: http://www.accessible-devices.com/IE7HotKeys.html

The only way to retain the values is if they have been assigned in the value=""...