diff --git a/ChatController/ChatMainControl.xaml.cs b/ChatController/ChatMainControl.xaml.cs
index 2b2d67b..66f2002 100644
--- a/ChatController/ChatMainControl.xaml.cs
+++ b/ChatController/ChatMainControl.xaml.cs
@@ -249,7 +249,7 @@ namespace ChatController
             notifyIcon.BalloonTipClosed += (sender, args) =>
             {
                 // TODO: wird beim ausblenden bzw. automatischem Schließen des "Balloons" ausgelöst
-                //DisposeAndRemoveNotification((NotifyIcon)sender, pGroupId);
+                DisposeAndRemoveNotification((NotifyIcon)sender, pGroupId);
             };
 
             _Group2NotifyIcons.AddOrUpdateValueInDictionary(pGroupId, notifyIcon);
@@ -276,8 +276,7 @@ namespace ChatController
         {
             pNotification.Dispose();
             _Group2NotifyIcons.Remove(pGroupId);
-
-
+            
             Application.DoEvents();
         }
 
@@ -732,6 +731,11 @@ namespace ChatController
                     {
                         foreach (var newContact in contacts)
                         {
+                            if(newContact == null)
+                            {
+                                continue;
+                            }
+
                             if (contact.GroupId == newContact.GroupId)
                             {
                                 // ReceivedMessage kann null sein!
@@ -741,9 +745,15 @@ namespace ChatController
                                     contact.TimeStamp = newContact.TimeStamp;
 
                                     var selectedContact = (Contact) Clientlist.SelectedItem;
+                                    // Angemeldeter Benutzer
                                     var userOid = _Chat.ChatDaten.LoggedInUser.Response.User.Oid;
 
-                                    if (selectedContact != null && !selectedContact.GroupId.Equals(newContact.GroupId) || selectedContact == null || _IsInBackground && userOid != contact?.ReceivedMessage?.UserId)
+                                    var senderId = contact.ReceivedMessage?.UserId;
+                                    var receiverId = userOid;
+                                    var receiverGroupId = newContact.GroupId;
+                                    var selectedGroupId = selectedContact?.GroupId;
+
+                                    if(senderId != receiverId && (_IsInBackground || receiverGroupId != selectedGroupId))
                                     {
                                         ContainingWindow.Icon = Utils.GetImageSourceFromIcon(Resource.oC_favico_NewMessage);
                                         ShowNotification(newContact.Name, newContact.ReceivedMessage, newContact.GroupId);