Hi mstrat,
It's actually the other way around. You may have just made the Master Tier, but there are active events that you entered while you were still in the Pro Tier. If you entered the event as a Pro then you stay to compete as a Pro until the event is over. While you're still competing as a Pro in those events you will not be allowed to use Master clubs. This prevents you from gaining an advantage over the players that are still Pro and cannot use Master clubs.
You will compete as a Master for any events that you enter from this point forward (or any regular rounds that you play) and you will be able to use Master Tier clubs.