Zent...contrary to popular opinion, Market Makers have a high risk/ high reward occupation. They recieve orders from brokers to buy or sell for the broker's client and they are under pressure from the brokerage to fill the orders quickly. If they fail to fill quickly and consistantly, the broker will likely shift his orders to another MM. Also, MM's make money on the spread...the difference between the bid and ask. On high volume days with a small spread, the MM is obliged to move a lot of shares for a relatively small amount of money. Sometimes MM's will Move shares they don't yet have (short) in order to fill orders and keep the big houses (Brokerages like Ameritrade, Scottrade, etc.) happy.
After the smoke from such a frenzied period clears, the MM's will trade among themselves to get back to square one. There is a lot of risk for them if they have a large short position and have trouble covering. MM's can and do lose a lot of money. Of course on the average they come out ahead, or they would go out of business, but they aren't the "Evil Empire" that some of the uninformed like to think they are.
What you are seeing is probably MM's moving shares around to ballance the books.
jc
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