Muffed punt and second kick

[footballref]

Thought I had seen this posted on a message board, but cannot find it. What would you have here? I think it is R's ball where K falls on the second punt. Also, please list a rule reference, as that is what I am unable to find to support my answer.

Play: 4th and 10 from the K20 yard line. K's scrimmage
kick is short and is muffed in flight by R at the K30
yard line and bounces back to the K15 yard line where
the punter picks up the ball again and kicks a second
scrimmage kick from behind the neutral zone. The second
kick goes about 35 yards where there is no longer an R
player to receive a kick. The ball is recovered by K at
midfield.

Ruling?