Had the same problem at MCO recently. I arrived, cleared customs, and was wanting to go outside when I arrived at a security point. I thought I had taken a wrong turn and attempted to back-track but was told that was the only way OUT. To get to the street, I had to change terminals using the monorail located on the sterile side of security. Why were we considered to be on the non-sterile side after clearing US customs, I have no idea, since that terminal had no contact with the outside ?
In MCO, forget putting a cabin prohibited item such as scissors in your checked in luggage, because after arrival you will have to go through security with that checked luggage to get to your rental car.