I have a Pearl Izumi PRO vest from (tag says) Fall 2012, and except for the flapping at the shoulder/arm hole on fast descents it is perfect otherwise. While the front doesn't pooch up when I bend forward, the bottom/back quarter of the arm hole changes shape enough to let air under it when your arms are anywhere but straight at your sides. I just got used to it -- as it only became a nuisance at 30mph+ air speeds. It has a way better fit than any of their (PI's) other vests in my experience.

And to fix it I think (part of) the arm hole needs to have elastic so it takes the shape when bent over ... or it should have been cut for the riding position.