audio challenge when entered same no of characters validates

While using Audio challenge,when a user enters the same number of characters with the first 3 characters correct and the last one with a wrong character, it validates. This looks like a bug. Kindly validate. -- You received this message because you are subscribed to the Google Groups "reCAPTCHA" group. To unsubscribe from this group and stop receiving emails from it, send an email to recaptcha+unsubscribe@googlegroups.com. To post to this group, send email to recaptcha@googlegroups.com. Visit this group at http://bit.ly/1dkFnYd. For more options, visit http://bit.ly/P65DvS.