Focus plane tracking calculations for cinecamera moves wrong direction when tracked subject moves past lens and behind camera

If an actor moves behind the camera while being tracked for focus, the focus plane moves back away from the lens the same distance the actor moves behind the camera.

This leads to undesirable behavior on a virtual production shoot since fast-moving subjects that move from in front to behind the camera will cause a sharp rack focus even after they leave the camera frustum.

1. Add cinecamera actor to scene
2. Set Focus mode to Tracking and select object close to camera
3. Turn on Draw Debug Focus plane
4. Animate tracked object so that it moves from in front of the camera to behind the camera
5. Observe focus plane move towards camera lens with tracked actor, then move back away from camera lens as actor moves behind camera (should stay at camera lens plane instead)