Barbara (and Lactnet),
Thanks for the eloquent explanation!  I would add to your list that
intolerance to formula supplements or an allergen coming through
breastmilk can also be a culprit. As you described, babies learn to
associate feeding with a following stomach ache and thus only eat enough
to survive, not enough to grow.  (Michael Woolrich gave a great talk on
this subject at ILCA in 1995)

On this note, I had a collegue call me last month about a gaggy spitty
newborn who was so congested he had similar trouble feeding.  He also had
a skin rash and was extremely unhappy and crying frequently.  Father has
numerous allergies including food intolerance.  Stopping just milk did no
good.  Removing ALL milk and products containing milk brought amazing
change.  I think it would be worth a try on your tough case that you saw
yesterday.  I've also found this to help in some cases of reflux.

Natalie Shenk, BS, IBCLC, private practice in NW OHIO