Duplicated notifications

When a user has notifications for both "Comments to my answer" and "Comments to my comment" activated and has commented their own question all notifications for comments are received twice.

While this is fine, it would be nice if one would only receive notifications for distinct events.

How to reproduce:

1. Write an answer with user 1
2. Comment the created answer with user 1
3. Turn on both comment notifications for user 1
4. Comment the created answer with user 2
5. Observer that user 1 received two notifications