Traction wrote:anyway the penalty was given because the drivers never slowed down when the yellow flags were out
Actually it would appear that the penalty was for using DRS which indicates you haven't slowed down. And again the yellow flags were out, but the FIA were also displaying the green lights.
Why were the lights introduced? Because they are so much easier to see than the flags. Except in this instance they were displaying the wrong thing and the driver was penalised for it.
What should the penalty have been? For me either nothing, because of the fault with the lights, or a monetary penalty. It may not mean much to these guys but it's still a visible slap on the wrist for what was really a very minor infringement.