The semi-strong efficient market hypothesis states that
In semi-strong-form efficiency, it is implied that share prices adjust to publicly available new information very rapidly and in an unbiased fashion, such that no excess returns can be earned by trading on that information.
During the last few years the definition of 'very rapidly' has been changed and new information will be processed in milliseconds which, if semi-strong EMH is true, would make price discovery nearly instantaneous.
I have the suspicion that with HFT the reaction to news is fast but not necessarily correct and that a number of corrections happen after an event due to better understanding of the new situation. Note that in this situation these corrections are a reaction purely to the first news event and not to subsequent events.
I'm looking for references on this phenonomen because if it's true it must lead to trading opportunities and if it's false it would be strong evidence for the semi-strong EMH on short time intervals. The answer could include a study on the behavior of the order book after big news events and its relation to the price after a somewhat longer period.