I trade a lot of pairs. Sometimes it's intraday, sometimes they live for days to weeks. I set one up on 4/09 because there was a good value disparity as well as to capture a pending dividend on ABC. I traded some of it during the week, captured the dividend on 4/15 and then began scaling it down at the end of last week. On Friday I closed long 2,000 ABC and short 2,000 XYZ. Monday I covered 1400 on each side and then the remaining 600 yesterday. At 4 PM yesterday I was completely out and yesterday's statement reflected no position in either, long or short. Today the prices reversed and I began attempting to scale back in. I traded a few100 shares in and out and at +400/-400 I noticed that although I had confirms for all of my trades, my account page indicated that I was at +400/-199. Called the broker, got someone on the trading desk and got a bit of what seemed like BS - was told that there had been a buy in of 201 shares for shares that I was short on Monday that will settle on Thursday. Seems the broker that lent to my broker called the shares and my broker couldn't find replacement shares so there was a buy in. IOW, no notifiction until today. It sounded bizarre to me since when there's an imminent buy in of a short position, I get a bulletin around noon or so and have until late afternoon to deal with it or they will. The few times I've let them close, when executed, there was a trade confirm beep as well as a trade confirm. Today, nothing. I questioned how I could be flat yesterday, get no warning to cover and get no confirm that they had bought to cover. I was promised a call back since they had to check with the clearing desk to see what happened. To their credit, they got back within about 15 minutes and I was informed that you can get a buy in execution any time until settlement even if you are out of the position. If I had not gone back into ABC and XYZ today, I would have found myself long 201 shares of XYZ today in the afternoon. Don't take this as sour grapes or the confusion of a noob. I shorted over 500,000 shares in the first quarter (and a similar number long). This buy in was good for $150 since I shorted the shares today at higher prices. What troubles me is that I've had much larger positions and because of the system, you can get screwed even if you do everything by the books. T+3 can shaft you