@karadoc I fully understand your logic about finded bugs, but sometime one fix could end up as rewriting some part of code to made everything work again. In my job I had couple times that situation, one fix exposed lot of other bugs in unexpected places. You should think about this "one line fix" as rewriting part of code.
Another thing is that calcualte line is used for tiles too (and there is copy of this function for path finding), one tile off would cause glitches that should be more visible than one vexel off.
@Meridian I will probably grab this code to my brach too (before 3.5) but I think it should end up in master brach.