I've a sub panel in my shop and I ran a new conduit down one wall in preparation for a saw station. There are two circuits in the conduit, that tie to two separate GFI breakers. I have independent power (black) and neutral (white) 12/2 strand, with a common ground (green) -- 5 wires were fished through. There are two boxes each with two duplex 20 amp receptacles. One circuit is on the left receptacle duplex, and the other on the right in both boxes. If I bypass the first box and only wire the receptacles in the second box (furthest from the panel), it works fine. If I wire in the first box, any load on any of the receptacles in the first box, it will trip both GFIs (a tester shows the receptacles are wired correctly). If I leave the first box wired in, and put a load on any of the four receptacles in the second box they all work fine. Any ideas?