When using the perspective tool the image canvas size never increases. This means that image data is pushed outside the canvas and cropped away. This happens without auto fill.
It would be better if the canvas size was increased in such a way that you are later allowed to crop from all captured data.
Usercase: When photographing a building in a cramped street without a shift lens (or uwa lens) you frame the image to capture the whole facade resulting in unwanted perspective in the facade. The ground is of no interest but takes up half the image. to avoid excessive loss of quality while resampling you avoid angling the camera to much upwards. When using the perspective tool you want to retain the whole facade but discard the ground. This doesn’t work with current perspective tool as the top of the building is pushed outside the frame where the data is lost.