Leaders don't coast!
A quick reminder on pulling a paceline ... you always pedal. Yes, that includes a downhill. You don't need to put a lot of pressure on the pedals on the downhill, but you do need to ensure more than just "spinning."
If you quit pedaling, surely all the others behind you will be breaking which is counterproductive for the paceline. It's just one of those rules: when you pull, you pedal.
Just do it.