vtkLabelPlacementMapper and vtkLabelPlacer incorrectly assumed at a couple of places that anchor point is specified in world coordinate system. This caused incorrect frustum clipping (randomly disappearing labels) when anchor point coordinates were specified in another coordinate system (for example: labelPlacementMapper->GetAnchorTransform()->SetCoordinateSystemToNormalizedViewport()).

There was also a small (probably copy-paste) bug in the culling bounds computation.