A new mechanism was added in 1.3.2 to supply an output clip for the effects so that they could reduce the amount of work that they perform. Unfortunately the PerspectiveTransform effect does not yet calculate the appropriate input bounds for the indicated output clip and so it forces its input to render its full size even if only part of it will appear on the screen.

(Note that, in addition, because of RT-9223 the PerspectiveTransform also does not clip its output to the indicated bounds either and both combine to cause it to behave poorly under large scale factors.)