I've noticed the same phenomenon in bush beans, and occasionally in pole snaps as well. It is normal, and as you have observed, the plants generally recover on their own (with a little TLC) and begin producing good pods again. Water stress (possibly caused by heat) could cause similar symptoms, but they would likely continue for a longer period, and picking off the stray pods would have no effect.

Plucking off all over-grown or deformed pods does seem to help trigger the second flush. My theory is that after the first flush, the plant needs to shift from a reproductive stage (ripening seeds) back into a vegetative stage (growing new leaves & buds). Its a question of how the plant chooses to direct its energy. Any ripening seed still remaining on the plant might delay that transition. Once the plant shifts to vegetative growth, it appears to abort immature pods... hence, the hollow pods. That's my theory, for what its worth. ;-)