The mystery remains...!, page-10

It has nothing to do with true market value, Vanguard is simply playing the game. If you look at the Shorts on SLR it is about 2%. At about 1 billion total SLR shares that means they can borrow and sell 20 million slr shares, crash the price and slowly buy back at the lower prices that they crashed.
They simply pocket the difference.
The cute thing is that it is your shares that the stockbroker is lending to these vultures.