Automatically update email address based on email address policy got selected automatically

We have the option "Automatically update email address based on email address policy got selected automatically" unchecked on the mailboxes to have a custom email address added to the users and make it as primary.

Now we see that some how this is checked and the default address policy got forced changing the primary email id.

The check box was not selected manually neither did we run the command to enable the EmailAddressPolicyEnabledto True

What else can cause the option to get enabled. 

Thanks in advance.