warpPerspective gives unexpected result

edit

Dude. I attached 6 photos. Look at the upper right photo. Can't you see the four parts of the photo are discontinuous? And can't you imagine what the correct one should look like? Do you need more explanation on this?

Assuming a transformation is made from (0,0)(10,0)(0,10)(10,10) to (0,0)(10,0)(0,10)(15,10) on the image. Because only the bottom right point moves right, the pixels in the original image should stretch towards right. The more stretch in the lower part. They must not stretch to neither left, down nor up. Tell me if you need more explanation here. However, in the transformed image which WarpPerspective() resulted looks like the 6th photo in the attached. Please find the red horizontal grid I drew. The pixels in the original image actually shifted towards up!