Not so much a bug as a technical issue; when you use the range tool on iOS (iPad mini in my case but I'd imagine it's the same for any mobile) you cannot read the distance value because your finger is covering it up since it's on the leading edge.  Perhaps the distance can be separated from the endpoint by 50px or something so there's room for a finger under it or have the distance appear in the midpoint of the line instead of the end -- or have the range rule fade out or linger for a second instead of disappearing when the finger is lifted.