The plastic covered piece of steel with the bite out of it.
If the plastic bonded all over or just on the edges.
If just on the edges, its conceivable without actually having a personal look at it. That the plastic could move away from the metal during a low pressure moment and pust back toward the metal during a high pressure moment. Kind of like a air pillow but with the fuel itself being the cushion on both sides of the plastic.
Don't really have any idea , just throwing ideas out there.
Chris