Etiquette/ruling - Putting line (Russian Open)

Now I don't know if the TV coverage skews things because 8 footers on TV always look more like 3/4 to me, not that I would make them.  but recently to me it's looked like other players have been standing on the putting lines of other players, identified by the ball markers.

This was definately so on the 18th yesterday at the Russian Open when Sandelin clearly stood on the putting line of Danny Willet, of England, to putt out.

Now is there an acutal rule on this ? a gentlemans etqiuette standard ?  who is it merely that the players can ask each other and stand on the line if they want ?

Darren , I believe there is no rule on this just  etiquette, I suspect Danny had told him not to worry about his line.