Then you had a neutral to ground short, or another neutral related issue. I can assure you right now, the issue was not with the GFCI breaker.I've had trouble with GFCI breakers, as well - especially when the actual load is a long ways away. Not sure why... For instance, an outlet on a lamppost 100-feet from the house never worked.
Not that I don't agree with you... But seriously. You want to give me the exact length that this occurs at? The reason I bring it up, is because I've never witnessed this in the field... I use a meggar and always find an insulation break down.For very long runs beyond a ground fault circuit interrupter, induced currents (due to capacitance) between hot and ground could be sufficient to trip the GFCI.