Can't schedule appointment for one service if same time is booked other Service

Hi. We have 3 services (no service providers). We have found out if a time slot is booked for Service #1, and someone tries to book a DIFFERENT Service (like #2 or #3) for the same time slot, the Calendar does not show that time. We have Capacity set to "0", so what would cause this? Please see http://screencast.com/t/BECVwmPRee

Thanks