One thing does bother me about all this capacitive coupling. Wouldn't BOTH current carrying conductors couple to ground a similar amount and if so the net current differential across the CT in the GFCI would be close to zero? In fact the current in the ground wire would null too.
I just can't imagine this is a real world problem when I see those T poles with 2 or 3 cube taps in them and hundreds of feet of extension cord plugged in. Certainly they trip now and then but I think that is more a function of the lousy cords and defective tools.
