So far, if a nep's growing tip blacken or sever, it's due to root rot. It doesn't happen due during posting or repotting. The only way it happens is if you rip out all the roots (which I don't think anyone would be willing to do!
) or if the media you use holds too much water. My veitchii was a good example. Too much peat and overwatering caused the growing tip to blacken. A second one appeared which made two normal leaves (no pitchers) and then it slowly recovered. Phew....