Feedback activity notifications do not respect separate groups if a user is ungrouped

We've noticed some behaviour we don't think is correct with the 

With multiple users on a course

User A is in group 1
User B is in group 2
User C is not in any groups
A test teacher is in group 1

All users submit to a feedback activity - the teacher gets notified for User A and User C - we don't feel that User C should trigger notifications, or this should be optional.