Dreamcather explained it a few weeks ago as follows
In case anyone one is wondering why the 8,302 share order that went through at 10.56am didn't effect the last sale price, it was a National Best Bid/Offer Crossing Trade.
National Best Bid/Offer Crossings do not update official prices such as open, high, low, last or closing prices, however, they do update the daily trade statistics of volume and value only.
