force removed or runner out?

Question
here's the situation (from a slow-pitch softball game):

   runner on first base, nobody out.

   batter hits ground ball to shortstop.  for some inexplicable reason, the runner on first base just stayed on first base.  the shortstop throws the ball to first base.  the first baseman catches the ball with his foot on the bag, but does not touch the runner.  the batter never made it to first base.

   obviously, the batter is out.  the question is:  what about the other runner?

   we thought that the force play on the runner was removed when the first baseman caught the ball from the shortstop with his foot on the bag.  thus, the runner should be safe on first.  if, prior to stepping on first base with the ball, the first baseman had tagged the runner, then the runner of course would have been out.  but that didn't happen.  (the rule book appears to say that the only way the runner originally on first base can be forced out is by tagging or by throwing him out at second.  neither of those things happened.  the rule book also has several cases involving two runners touching the same base.  but that never happened either, because the batter never made it anywhere near first base.  

 the umpire ruled that the runner was out since he was forced to advance once the batter hit the ball.  but i couldn't find anything like that in the rule book and think he just made that up.  in any case, we were saddled with two outs instead of just one.

who's right?

Answer
Hi luke,

Well R1 was "forced" from 1st base and had no legal right to occupy it....until the b-r was put out.  Once the b-r was out there is no longer any force on R1 and they can legally occupy 1st base.

this would be correct "we thought that the force play on the runner was removed when the first baseman caught the ball from the shortstop with his foot on the bag.  thus, the runner should be safe on first."

Just as you also say if R1 had been tagged 1st (on or off the base) they would be out and then step on 1st base for the 2nd out.

The umpire was very incorrect in this and you could have brought out the "P" word.

Mark