Vanishing spray is new to the Premier League so the referees haven't quite figured it out yet. As in which way it sprays.
You may think it's as simple as looking at what direction the nozzle is facing and then points that at the patch of grass you want to mark, but it's not. Sometimes faces get in the way and you assault yourself and a player. It happens.
This is advanced technology, new to the sport in 2014 and it has not yet been harnessed. Technology is a tricky mistress.
Sometimes you spray people's feet.
The referees are making so many friends.