MailPoet Not Adding Subscriber

Thanks for MailPoet which is elegantly designed. ??

Our WP site is set to allow different users to have the same email address, but a different WP site username.

A batch of subscribers was imported to MailPoet via csv, no problem.

…but now, when I try to add a single, new WP User (as a subscriber) to MailPoet (a WP User who has the same email address as a current, different subscriber at MailPoet) manually, the new subscriber is not added to MailPoet. Instead, the details of the subscriber already there, with the same email address, get updated, but no new MailPoet subscriber is added.

Does this mean that MailPoet can only handle one subscriber per email address?

Thanks for your advice.