If a mirrored configuration has a 'letterbox' effect (i.e. inbuilt and external screens have a resolution mismatch, and secondary screen shows black bars on top/bottom or left/right), then the 'paused' screen will stretch the captured image to get rid of the black bars, but will distort the image as a result. This was discovered on a device with a 1920x1280 inbuilt screen, connected to a 1920x1080 external monitor - by default, the inbuilt screen kept it's native resolution, but showed on the external with black bars left and right of the picture.