In some cases when you fall from safe distance horizontal movement adds to the overall falling distance making you lose health/die. I haven't found further details in which situations this occurs.
You could be referring to the same short-distance-fall annoyance people have observed for a while. I've found that I can almost reliably make the "safe falling distance" not-so-safe. If I'm coming out of a tunnel at the top of a room (i.e., moving horizontally
like you described), try to make a short jump, bump my head on the ceiling, and then fall to the floor, it hurts. If I don't bump my head, I'm okay.
Or am I making a big deal out of superstition and chance? I don't know!