ARCA is quite disappointing. Glad someone started a thread on this, perhaps they listen into these disquite-ing thoughts and will improve or acquire another ECN.
I have posted many a caution and notice against these smart order routing features of these ECN(s) because in these choppy markets, where we are essentially trading against phantoms, having one's order posted, displayed, HELD for nn-seconds and then cancelled or DELAYED-Executed is detrimental to one's profitability.
Sometimes the delayed execution notification is delayed itself, and you end up over trading your position and getting tagged for forfiture of profits from illegal short situations.
Hey, ARCA's got a long way to go, as well as a few of the other major ECN(s).
ISLD rules!, as well as the others which DO NOT hold the order, either from cancellation, modification or delay from execution.