Select contact auto-complete - should throw formRule error if user replaces an existing contact name by typing in another value

As reported here:
http://forum.civicrm.org/index.php/topic,11122.0.html

Affected forms are New Event Registration, New Contribution, New Membership, New Case, New Pledge, New Grant.

If you initially select a contact name from the drop-down in the "Select Contact" auto-complete form, but then type over that name with another name (which doesn't match to an existing contact), the postProcess uses the initially selected contact ID to create the Participant, Contribution etc.

This should be fixed so that the contact_id is cleared in the field value when the user types over the selected name - which then would produce the correct result for this sequence.... a formRule error is thrown:

"Please select a valid contact or create new contact"