Another problem with stuff from the official documentation. Might be the same reason.
Registering and Unregistering triggers does nothing.
With a sample trigger called SampleTrigger, I've got the following code to test the feature.
CharacterApplyStatus(_Player, "BURNING", 1.0, 1);
CharacterApplyStatus(_Player, "PETRIFIED", 15.0, 10);
As you see, if a character enters the area, the trigger should get unregistered for them, causing the LeftTrigger event to be fired, so they first turn to stone and then burst into flames. That's what the official documentation says, anyway.
It doesn't. People get properly petrified if they walk out of it, but if they walk in, the unregistering does not cause the second part to activate. Repeated walking into the trigger by the same character also causes them to combust repeatedly, unregistering notwithstanding.