Object update used to free object-data level bounding box to trigger it's re-calculation in the future. Such a freeing performed from object update isn't thread-safe because mesh could be shared between multiple objects. Rather than freeing bounding box, tag it's as invalid, this is safe from threading point of view and also prevents unnecessary memory re-allocation. Object-level bounding box is still reallocating, but think we could change this easily in the future as well.