I went outside just before the sun went down and caught some pictures. Here is the evidence on the patio, along with fallen blossoms.
This picture shows two pods, one unopened, and one and seemingly just waiting for the wind to bring its seeds down.
At right, one seed sticking out from its pod, holding on by a thread.
It must be a complicated formula that tells the pods when to burst open, or a certain number of hot and cold contractions, combined with humidity, that determines why some shoot in the spring, and some in the fall.
One September our neighbor whose yard backs up to ours phoned us after dark and said, "I am really afraid; it sounds like someone is shooting at my house!"
We told her it was the wisteria. Hers always blooms way earlier than ours in the spring, being on the east side of her house, while ours is on the west, and in its own tardy micro-climate. They probably do their seed-scattering alternately as well.
We are kept busy pruning or sweeping, smelling or listening to this vine through all the seasons of the year. It's a great back yard resource!