I like trading on IDEALPRO, but there's this thing that's been bugging me recently: The great thing with an ECN like IDEALPRO is that you participate in the market and can trade against other customer orders, not just the banks (or THE bank in case of a dealing desk). But in the volatile environment this week and the one before, I've seen a couple of times that my order is resting on the bid-side - best bid and all alone - and then witness a market-maker (as by the size in millions) briefly rest on the other side of the same price, before bouncing up a pip or two again. I should have been filled with STP, but didn't. Now I'm not really complaining much about it, but I'm wondering: How can IB disseminate a quote and then not trade against it? I am positive I was alone bidding at the price level, and I don't think they allow invisible orders to trade in front of me (?). I'd appreciate if anyone from IB could either comment on what this was, or whether they claim it was a mirage. Or anyone else chime in for that matter.