Group subscriptions are reset after contribution/participant signup

Say a contact is already in the db, with email joe@test.com, and is subscribed to the newsletter group.

As a non-logged-in user, Joe decides to make a contrbituion. He inputs his same email address which will cause him to be matched to his existing contact record. This contribution form happens to offer a newsletter subscription option (via "groups" field in a profile).

The "newsletter" checkbox will not be checked by default because Joe is not logged in. So Joe can do one of two things:

1. He can ignore the checkbox (assuming that since he is already in the group there's no need to check it again). This will cause him to be silently unsubscribed, with no warning or confirmation.
2. He can check the checkbox. This will change his status from "Added" to "Pending" and will send out a new confirmation email. If he ignores the email (as a frequent donor they might be quite annoying) then he will never be resubscribed to the group.

IMO both of these behaviors are wrong. An anonymous user ought not be able to unsubscribe from groups from an "opt-in" type of form.