Foul Bunt on an 0-2 Count

 
With no outs and an 0-2 count on the batter (B1), the runner on first base (R1) is stealing on the pitch. Surprisingly, B1 bunts the pitch. The ball slowly rolls down the third base line, but eventually rolls into foul territory where it is touched by the third baseman. The play ends with R1 at second base and B1 at first base.
 
What do the umpires do with the runners on 1st and 2nd base?
 
Call
If a batter attempts to bunt with two strikes and it results in a foul ball, the batter is out. On a foul ball, the ball is immediately dead and the runners must return to the base that they occupied at the time of the pitch.

In the situation below, B1 is out and R1 must return to first base.