infield fly and interference

Question
Runners at 1st and 2nd one out.  Routine popfly towards SS R2 breaks towards 3rd and collides with SS just prior to the ball being played and ball falls to the ground.  Batter is out on the infield fly rule, but the umpire allows play to continue, ruling that the contact was incidental and both runners advance.  Because the infield fly is in effect to protect the runners and she was clearly advancing, shouldn't have R2 been called out for interference, giving us the double play we would have had, if there was no contact?

Answer
Hi Charles,

I'll pick this one up for you.

I don't know how the contact can be incidental, the defensive player must be given the opportunity to field the ball anywhere on the playing field w/out being hindered (I assume F6 is attempting to catch the infield fly).  The offensive player must vacate any space needed by a fielder to make a play on a batted ball (except if legally occupying a base and then they must not intentionally interfere)

I have interference, a dead ball, R2 is out and R1 is returned to the last base touched at the time of the interference.  The fact that this is an infield fly doesn't matter.

Mark