I think it might have followed Jack because of that little one on one moment he had with her..she was totally taken in by him in that scene..ignoring everything..she clearlyy loved the attention she was getting there..
and every scene after that where Jack is really close to her..the compss points right at him lol
I have a feeling that it points and sticks to where Jack is..then he moves to the other side..I think that it points and once it has stuck it doesn't move..until its closed and opened again..IMO anyway..otherwise if it was pointing to Jack on the pearl an then he moved away I bet it wouldnt follow him once it had stuck..
oh I dont know..I just find it strange how when ever Jack is very touchy feely with her the compass starts to follow him or actually sticks on him..