For those of you that are running into this problem, it seems to just snap off at the root. Is the rest of it brittle? Can you break it halfway down the mane, or is it just weak at the root plug?
In my own experience, it's brittle all the way down, but I've only run into the "rotting" pink and peach, not any other colors. (So far!) I think it might break at the root so often because there's a lot of bending near the plug line, thanks to gravity, so that might be a natural weak point in the hair fibers. But even if you're careful not to put tension on the roots when brushing, the hair can just snap off mid-shaft.
I was resigned to the state of affairs with the discount ponies, but now that these things are being reported with new ones like Morning Glory, I'm really scared for the longevity of my G3s.