I have seen the problem of which you speak, Dustin, as have
others I know. Moreover, this problem is not unique to
N. northiana; it can occur with almost any species of Nepenthes.
My opinion is that it is caused by rapid shifts in humidity, and
can also occur as a result of inadequate soil moisture. Some
species, e.g., NN. tentaculata, macfarlanei, lowii, and rajah,
exhibit this tendency much more readily than other species.
If anyone has other thoughts on this phenomenon, I would
be most happy to see them posted.