Oh, that totally happens.

I actually have a character -- one of Carl Bernhardt's victims -- whose original male upper body has been grafted onto the lower body of a mare. Somehow, "dysphoria" just doesn't seem like enough. >_<

Meanwhile, people who work for the major companies cannot seem to figure out how to write your garden-variety MTF or FTM. Seriously, people? I was writing weirder stuff in junior high.