The 5100 share ask was automated. When any new sell order appeared in a given range, it would adjust to .0001 lower instantly (technically it's a new order and the old is cancelled, but we might as well view it as a self-adjusting order). With a fairly large spread as we had yesterday (and most of the time for the last few weeks or longer), these auto orders usually have a range that ends at the midpoint of the spread, if that far. This time though, it turns out that range extended as close as possible to the bid, which was then .1010.
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