Field properties ShowInEditForm not saved

Question

I have an listadded eventreceiver with the following code:

 public override void ListAdded(SPListEventProperties properties)
 {
    SPWeb web = properties.Web;
    bool safeUpdates = web.AllowUnsafeUpdates;
    web.AllowUnsafeUpdates = true;
    SPList list = properties.List;

    SPField VanField  = list.Fields.GetFieldByInternalName("MyFieldName");
    VanField.ShowInEditForm = false;
    VanField.ShowInNewForm = false;
    VanField.Update(true);
    list.Update(true);
    web.Update();

    web.AllowUnsafeUpdates = safeUpdates;
    base.ListAdded(properties);
}

The problem i have is that the ShowInEditForm and ShowInNewForm not saved to the fields.

The event is an sychronous event. THe field is an Taxonomy field, maybe that's the problem.