NOTE: this article applies to our older (V2) templates only. It does *not* apply to templates built with our multiple fields form builder.
When opt-ins are being sent via API, ConstantContact does not add them if they are present on one of your other lists already.
ConstantContact's API (the system we use to integrate with LeadPages) is designed to check if an email address that we send is on *any* of your lists already. If that is the case, the email is being treated as already subscribed and is not being added to your (new) list.
This a policy by ConstantContact and our previous form builder follows it. In other words:
If you want to have the same subscriber on multiple lists, you will have to use a multiple fields (V3) template
If you found this article helpful you may also want to read this article: Why is the LeadPages optin number different from the optin number in my email service?
If you have further questions, please file a support ticket. :)