Users never get added

[djmtype]

Sign up using hidden field

I'm having the form send using the hidden auto-subscribe field.
Example: [ctct ctct-163 type:hidden 'Master List::#2']

The user only gets added to the Constant Contact list so long as the email address has never been submitted before.

Meaning, if the email address was first submitted using Contact 7 and this plugin, then deleted from Constant Contact, then submitted via this plugin again, it will not add the user to the Constant Contact list. Why is that?

Sign up using check box

If I include the check box, the issue I detailed above is no longer a problem. However, in any case, Constant Contact's auto response Opt-in message is never sent to the user. This setting has been enabled in my account. And I've verified it works with Constant Contact's forms.

How do we display the check box as marked by default?