I don't know all the whys, but I do have some experience with hows and
whens.....
In my experience, the key is the thickness of the bread--nearly any thin
bread, about 1/8-1/4 inch thick, will try to puff up if baked on a very hot
surface, like preheated bricks in a 450 or hotter oven, or on a hot griddle
or frying pan on the stove. It does not depend on gluten, as corn
tortillas puff up on a hot griddle.
This is why most crackers have holes poked in them--to keep them from
ballooning during baking and why many flatbreads are dimpled by fingers or
pricked with a docker device.
My guess as to why is that when a bread is thin and baked fast on a hot
surface, the little bubbles inside more easily coalesce into larger
bubbles, which grow rapidly under the quick cooking conditions into one
large cavity. A thicker bread wouldn't be cooking so fast, so the bubbles
might not be so prone to rapid growth and rupture to join in the bigger
bubble cavities--although you do often get bigger bubbles just under the
surface skin of some larger loaves, it doesn't propagate through the whole
thing to make a hollow loaf.
Diane Brown in St. Louis
http://www.well.com/user/debunix/recipes/FoodPages.html