Occasionally, one leads information may be shown when the form has pre-fill enabled. There are specific circumstances where this is possible, and it is most common during testing. These articles outline the scenarios:
However, what if the information in the form is submitting to the original lead whose information was shown on the form?
Since the information originally shown in the form was from a cookie, Marketo assumes this is a known record. If no email address is included on the form (this is a bad idea), the data entered into the form will be submitted to the original record shown because there is not an email address to deduplicate against. The solution is to ensure there is an email address on the form. This also prevents leads who are unknown from filling out the form and creating a record in your database with no email address.