I have had it happen twice where I placed an open order for SC (Siamcoin) to be sold, turned off my computer and then the next morning logged on to Poloniex and found that my open order had not been sold during the night when the price had established itself at the sell price I had placed. Do I have to be logged on to Poloniex in order for an open order to be placed?
Scott
lets make something clear about "price had established itself at the sell price I had placed" part:
for example if you placed at order to sell something at 10,000 satoshi and price went above 10,000 (like 10,001) satoshi and your order was not filled then that is a problem.
but if you placed it on 10,000 satoshi and price went to 9,999 satoshi obviously your order won't be filled.
also if price went up to 10,000 exactly and your order was not filled, it can still be understandable because your order was in a queue and there were other orders in front of you at the same price that needed to be filled.