You and me both, Skip. Does it matter where the ball was fumbled? The initial play says, "He starts to run it out but fumbles", so I'm not really sure "where" he was when he fumbled. If he was out of the EZ, no question it's a safety, but if he was still in the EZ when he lost possession, and the fumble was subsequently recovered in the EZ, the responsibility of the ball's movement is clearly the fumble, which was never grounded to acquire a new force.
Since the ball was fumbled in the EZ, and subsequently recovered in the EZ, with no new force involved, wouldn't the result be a touchback? It doesn't seem that wherever the ball might have gone while it was loose makes any difference so long as nothing happened to it to create a new force, which we agree was still caused by the fumble.
Since a new force is not a factor, this play seems the same as a situation where the fumbled ball rolled out of the EZ, and then rolled back in under it's own momentum before it was recovered. The material spots seem limited to where the ball was fumbled and where it was recovered.