Shorts put up bids for the exact amount to match another trade at the ask. They are for the most part working in collusion which may be illegal. The idea is to give the illusion of a sell off when if fact, the majority of trades have been above the closing price. market makers are actually allowed to do this. It is not fair but many things in the stock market are stacked up against the retailer. If the MMs are doing this in this specific situation, they are abusing their privileges. In any event, most kerx longs are well aware that the MMs " paint the tape" on a regular basis out of sheer desperation to try and scare people since they have been caught short for 5 years. So, in this case,it can work against them since it makes more astute investors who are aware of the situation more wanting to buy shares and hold for a big pay day brought on by a squeeze from their desperation!
Are you talking about the 6.43 Low trade? Those aren't trades that go through at the bid/ask. Usually stuff like that is larger firms that have negotiated the price during the day and settle the trade after hours. At least that's my take. I see it all the time, and the bid/ask spread never change on the after hours books when trades like that go through.
My guess is that mutual funds tend to swap shares at the end of the price for a prearranged price (for instance, at 9:30 they said "we want to dump kerx and so we'll take the current price, but just execute the trade at the end of the day.).
So I don't have any real evidence of the above, other than seeing it all the time without being able to ever see those bids/asks on the order book.