A Formal Double Camellia is one of the most desirable Camellia forms of the entire Camellia family. They can be a very tightly formed flower or they can be loose formal double, often referred to as a Rose Form Double. Most true formal double flowers don't open to show stamens. There are some that may start as a loose formal double then open to show scattered stamens.
In some very warm climates, formal double flowers may not perform well and they also can have problems if the weather warms too suddenly in cooler climates. They could form a ball - where the petals get all tangled up inside themselves when they try to open and they get stuck. This condition is often called 'Balling' or 'Bull Nose'. Usually the flower falls from the plant. This doesn't happen just to formal doubles, it can occur with any large flower with lots of petals and can be climate or genetic.