Because they can I guess, someone wants to keep this down for some reason. There were over 14 sells below the bid price today and they all happened when the PPS was getting positive traction.
panic sales drive down the price and then they can buy back in cheap. It only takes 1 transaction at the bid to lower the price. If the bid is 3 ticks down, it will lower it 3 ticks on 1 share traded. People panic and next thing you know they have some cheapies and it shoots back up. Easy money.
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