Save user id along with new contacts in order to correctly filter them out via CanCan later on.

app/controllers/contacts_controller.rb

@@ -62,6 +62,9 @@ class ContactsController < ApplicationController
       end
     }
 
+    # add the user id for CanCan
+    c.user_id = current_user.id
+
     if c.save
       flash[:notice] = 'Kontakt hervorragend angelegt!'
       redirect_to :action => 'index'