What's the match-score threshold?
Most fingerprint scanners (capacitive, optical etc.) still operate on match scoring based on the fingerprint and stored match points from initial enrollment of the users print. Maybe Ultra-sonic scanning uses a different comparison method, but if not it sounds like the score threshold was too low, or the initial enrollment allowed for a data set small enough that more than one print could successfully authenticate.
Either way, bravo to Mrs Neilson for the find :)
Biting the hand that feeds IT
