I see this difference has been happening in the past few months but I have not seen the witnesses handle this kind of aquilion. When poloniex can not deposit SBD and Steem then the price start somewhat stable but if poloniex and bittrex together we can deposit sbd and steem then the victim remain in poloniex. Because that dipoloniex deposit more than bittrex. The witness should be able to balance the deposit between poloniex and bittrex so that the price of these two websites can be balanced.