sharepoint eventreceiver and alert filter not working

Question

have a strange behaviour with alerts on my sharepoint site.

I have a document library where i want to add alerts to specific users when adding,updating,deleting folders or documents. Alerts must not be triggered for a specific user.

ItemReceiver :

 public override void ItemAdded(SPItemEventProperties properties)
     {
        AlertManager manager = new AlertManager(properties.List, properties.Web);

        manager.UpdateAlerts();

        base.ItemAdded(properties);
    }

I have a method where i check if every user of a certain UsersGroup already has an alert or not. If not i add one.

The method which add alerts :

 private void CreateUserAlerts(SPUser user)
    {
        SPAlert newAlert = user.Alerts.Add();
        newAlert.Title = "AlertTitle" ;
        newAlert.AlertType = SPAlertType.List;
        newAlert.List = currentList;
        newAlert.DeliveryChannels = SPAlertDeliveryChannels.Email;
        newAlert.EventType = SPEventType.All;
        newAlert.AlertFrequency = SPAlertFrequency.Immediate;

        string userFilter = "userLoginNoTriggerALert";

        newAlert.Filter = "<Query><Neq><FieldRef Name=\"Author/New\"  /><Value type=\"Text\">" + userFilter + "</Value></Neq></Query>";

        newAlert.Update(true);
    }

For every first folder/document added the alert is triggered as if the filter isn't taken into account. But then everything work as expected after.

If anyone has an idea.