Default values for list signup are used upon profile updates, not just when creating new users

I see the same happening after a long debugging session. I wanted to unsubscribe users when cancelling their accounts, so I wrote the following piece of code:

<?php
/**
 * Implements hook_user_cancel().
 */
function MYMODULE_user_cancel($edit, $account, $method) {
  if ($lists = mailchimp_get_lists()) {
    $list = reset($lists);
    mailchimp_unsubscribe_member($list->id, $account->mail, TRUE);
  }
}
?>

When cancelling the user I see them being removed from the mailchimp list. However, a second later, they are re-added again.

This happens in _mailchimp_lists_field_postsave().

I 'fixed' it by leaving the default value empty, and subscribe users by default using the following code:

<?php
/**
 * Implements hook_user_insert().
 */
function MYMODULE_user_insert(&$edit, $account, $category) {
  if ($lists = mailchimp_get_lists()) {
    $list = reset($lists);
    mailchimp_subscribe($list->id, $account->mail);
  }
}
?>

However, it would be better if the Mailchimp module only uses the default value when creating new users, not updating existing users.

I have an issue whereby the default value is ignored on creating new users. It was working but appears to have just stopped. I've just updated to 7.56 core and 7.49 module but the problem persists. Originally we had it configured so so MC field was hidden from the user registration form but still had the default value of subscribed and it worked fine. Now the only way it (sort of) works is if I expose it on the user registration form - the box is ticked. However if I hide it from the user registration form and sign up as a test user, I'm not subscribed by default. I've tried changing permissions and other settings but not getting anywhere.

Is this a known issue? The strange thing is why it was working fine for so long and just stopped. Maybe something at the MC end changed?

Thanks in advance.

Ok there's a nice rules integration for this in my case so I just set the default of the field to off, created a rule to react after saving a new user account and set the action "Subscribe or unsubscribe entity from a MailChimp list". Seems to work well.