Actually there is another more obvious blooper in that scene - when Danny starts arguing with his brother he pushes him against the well, but the wall already has a big dent in it, obviously already there from the rehearsal/run through.
OP: good for you. Better fire that continuity girl.
What I love in that scene is the fact that you can see at one point that Williams really hurts Lawrence. I believe it's just before he says "And in his heart your father sees it." His pained grimace when Williams' punches him in the gut is obviously real.
Loved POTC when I saw it at that little theatre in the basement of the Plaza Hotel in 1981, and love it on DVD today. Still have the soundtrack that I bought at the old Doubleday's on 53rd & Fifth. Phenomenal score, phenomenal film.