I had this problem today and solved it by using the plastic that comes off the adhesive tape around the edges of the digitizer, cutting it to size and laying it on top of the foam seal on each side of the screen and then turning and cutting the plastic from the top and bottom and sticking it to the base and top of the screen.
It seems the chassis of the iPad mini is magnetized, which you will see when you screw the metal shield plate in and the screw disappears from the end of the screwdriver.
I dont know if this (the magnetism) is the problem and im no fizzy-sist but shielding the edge of the digitizer seems to solve it, for me.