Last friday, I found a interesting thing. I reserved 1000 shares on arca, and then reserved another 1000 shares on arca. After 2 minutes, I got filled by 200 shares. But I found I have 900 shares reserved on first arca-order, and another 900 reserved on second arca-order. How is that possible? I thougth I should have 800 shares reserved on first arca-order and 1000 shares reserved on second one. Any comment?
Generally speaking, for a given price level, the displayed portions of all orders will be executed before the non-displayed portions...You had 100 shares displayed and 900 hidden on each order...so 100 shares got executed from each order first (displayed portions)