PK Situation
 

PK. Blue team kicking on red keeper.
Blue 13 kicks, ball hits crossbar and ricochets high into the air with lots of backspin.
Red keeper, thinking PK is over, rushes away excitedly.
Ball now descends with backspin and, you guessed it, hits the ground and starts heading toward goal line as Blue keeper hustles in to get into position for next kick and picks up the moving ball and, thinking nothing of it or so it appears, tosses it back to the ref.

What to do?

KFTM ended as soon as blue keep touched it. Move on.

And instruct the blue keeper not to touch the ball when it's in motion again.

Could he be ejected for DOGSO!! LOL

Imagine that.............the ref ejecting the blue team's GK for DOGSO of his own player!! That would go down really well!! lol

Did you try to yell at the Blue Keeper to stay away when he/she started towards the ball? Before a tie-breaking PK I usually tell both keepers that the ball is not dead until in possession of the keeper, is out of bounds or the momentum of the ball has died. Hopefully they get the gist of what I mean.

Also, the official who was standing on the goal-line outside of the post, who should be in front of the current kicking-team's keeper during PK kicks, should have told the keeper to wait to see where the ball goes.

Why would you do that? Would you tell the kicker not to touch it again?
Don't provide instruction to the players. That's not the job of the referee.