I am guessing that Sydney has put in a mechanism to validate the user (somewhat as we have had to do also here at the University of North Carolina). Our modification does not use any of the standard methods for tokens (other than the token itself).
This appears to be a design issue with LimeSurvey - and I agree with you that there does not seem to be a necessity to have the survey taker to re-enter their information. At best, I would think that an email address presented to the survey taker for validation would be sufficient.
You may want to submit a feature request at
ideas.limesurvey.org/