In terms of getting stopped out, that's interesting. I am pretty certain the ticket price which is leading the graph will stop you out if it reaches your stop level before the price chart does. I think IG will definitely be activating stops on the leading BUY SELL prices, not the lagging chart prices, but I don't know for sure.
Its just that when you enter a trade, you get the BUY SELL price, even if the chart is saying something else.