I've used the MailChimp API for my site's main newsletter subscribe form (embedded in a sidebar widget) and haven't noticed this happening - all of the people who sign up via the form are added to my MailChimp list.
Now I'm running a couple of giveaways that I want to make exclusive for subscribers to my newsletter. This may not have been the way to go about it - maybe I should just use MailChimp to verify that a person is or isn't a subscriber. But here's the form, and what I did was to create two email fields. The first one is just to enter the giveaway, and the second one is conditional upon the answer to the question "Are you already a subscriber?" If the person answers "No," then they have to fill out a second email box which includes "I understand that by filling this out I'm subscribing to your newsletter" verbiage.
I've mapped the field for the SECOND email box to my MailChimp feed, and what I've noticed is that about half of the people who click "No, sign me up" and fill out their email a second time are added to the MailChimp list. The other half - aren't. But they're showing up in my GF dashboard as having filled out their email addresses a second time. Everything seems to be exactly the same as far as people who were added versus people who weren't.
Is there some other setting I need to change?
I'm also wondering if there's a better way to create the form such that people don't have to enter their email twice to enter the contest if they're not subscribers - but people who are subscribers already don't end up being subscribed twice...maybe I should just count on MailChimp to screen them?
