Hi there

When you have someone on your contact list and want to put this person into a group per drag and drop, then this person gets the message "Xy has added you to their contact list."

As the person is already on the contact list, I would think, this is a bug.

Probably the game doesn't really handles groups correctly and when dragging someone into a group, it just creates a "new" friend and sends out the message. The person stays in the other group/no group as well when dragging.