I should know the answer, but . . .

[debeau]

Yes I can see that.
Under ISF rules the definition of IFF is given (same as ASA) then under notes it says "When an IFF is apparent the Ump shall immediatly call Infield fly if fair batter is out , for the benifit of the runners .
This goes with you logic that if not called then you put the runners in jeopardy and if put out then you correct the call and put the runners back but if runners are safe you leave them where they are and no outs .