Things seem to be a little mixed up on this page. You are setting the redirect in the update behavior to the session variable. This should redirect you to the page in this variable when the update occurs. After the update you have the custom code to check on the posted values and redirect based on that. If this is how you would like to do the redirect you should remove it from the update server behavior.
Also, the custom redirect code that you have is not using the same trigger, so it is possible that a form post is occurring and not triggering the update but triggering only the custom redirect code. You should update the triggers and make them the same so that they will both execute in order when the trigger occurs.