Weird Behavior Between Assigning a Contact and Adding a Phone Call

Hi,

I've experienced a weird bug while working with dynamics. If a user assigns a contact to him/herself, and then adds a phone call for that contact, all activities on the social pane change to being "completed" by the new "owner" of the contact. This only occurs when a user 1.) Assigns herself a contact, and then 2.) adds a phone call. 

Has anyone else experienced the same thing or something similar? Does anyone know how to solve this problem?

Thanks very much for any help.