I can't speak for any particular camera, but any camera that lists a maximum flash shutter speed has a curtain type shutter.  One curtain opens, then the other curtain closes.  At shutter speeds faster than the maximum flash shutter speed, the second curtain starts to close before the first curtain has fully opened.  In other words, the entire frame is never exposed to the image forming light simultaneously.  The same "painting of the image" that happens at high shutter speeds with a curtain type shutter would cause some of the image distortion effects you are seeing.  Some of the shutters move vertically, some horizontally.  They are also called focal plane shutters.

 

Mike Easley