I wonder if a blind section of seat post, dropped into the seat tube,
wouldn't hold up the main seat post, with very low QR torque.
This makes sense for setting the seat height easily. But it only obstructs the seat pin from moving downwards through the bottom QR. If the QRs aren't tight enough to hold the seat pin, it can still move up through the bottom QR then down again, and up or down through the top QR as the bike flexes. This chatter could fret the frame or seat pin.