Its the way the closing match ups work. A lot done by computers....

Its the way the closing match ups work. A lot done by computers. example:
Yesterday there was a buyer for 20,000 at 1.7 c ...

There were say 100,000 for sale at 1.7 c. So another seller has to go behind the 100,000k sell order. By putting them to sell at 1.6 they jump the queue.
So the buyer will pay 1.7 20,000 and the seller at 1.6 will get 1.7 , but a fraction of a second before it closes the buyer has order changed to 19,999. Which means then more for sale at 1.6 than buyers, so the whole lot goes through at 1.6.. so a buyer in the 5 million queue at 1.6 only has 1 share of his order filled,