Those that can, do. Those that can't, steal. F*ckers.
I've had this happen to me and it can be gut-wrenching. Years ago, a guy who was supposed to be writing a screenplay with me (never again, btw, I go solo), actually had me do all the work and then stole it from me. I lost out on a huge production deal, more than a screenwriter normally gets for a first feature. Hugh Grant was going to potentially star, etc. It got really ugly. That's all I'll say. And then a few years later, a producer "adapted" an original pilot I sent him. "Adapted," in that he stole the whole thing. For we writers who can't afford big-time attorneys who specialize in intellectual theft, this can be a terrifying minefield.
Great piece, Helen. Thank you.