Ciabatta texture problem
 

I used a new recipe to bake my first loaf of ciabatta in months. All went
seemingly well and it rose nicely in the oven but when I cut into it there
was a single, huge void running along almost the entire upper half of the
loaf. What I want, of course, is a nice, open-textured ciabatta, with
something like a third to a half of the loaf consisting of
pea-to-marble-sized voids evenly disbursed throughout. You know, like what
you buy in the store. I've had the same problem once or twice with plain
French bread as well. What causes this?