Hi Marc,
Ok, I understand now.
First, since you're with V9.0 (from other questions), I assume you know that by using the Application.Forms.GetEventForm(formId) function, you'll get an EventForm specific to the current form, so you'll avoid to deal directly with the application.FormEvent.
I'm surprised that the Form.Update doesn't work... I'll find a moment this WE to have a look at this 
Regards,
Eric