We don't use the X-Plane engine model whatsoever, we are setting the override flags with X-Plane so we provide the engine forces out to X-Plane. From my understanding, X-Plane still runs the underlying default engine model in the background (that doesn't do anything with the rest of the aircraft) and what you are seeing here is whether the default engine model run.
If OneAir has any other dataref that can be set for the engine status, I can look into that, but if all they are looking at is a non-writable dataref there isn't anything we can realistically do that wouldn't add a whole level of complexity to the product.