Infield Fly question

[justcallmeblue]

situation:

R1 on 2B, R2 on 1B with noone out. . .Batter hits Infield fly and Infield Fly is called by the umpire. SS drops the ball unintentionally (sun) with BOTH runners 1/2 way to their next base. . . .after the drop, both runners safely advance to 3rd and 2nd respectively but they do not tag-up. . .

I was the pitcher in this game and I am also a new ump. I appealed both runners thinking they have to tag-up. Ump called both runners safe because Runners do not have to tag up on a DROPPED Infield Fly. . .is this correct???? Otherwise, I had my first triple play!!!