This still happens to me too on my work machine, Win7, two monitors, build 2206. In case it matters, my primary screen is 1920x1080, and my second screen is 1440x900.
If I drag a tab off of the ST2 window and on to the desktop, the new window seems to always be created at the same X position where I dropped it, but at a Y position well below the screen.
With that new window as the active one, I press Alt+Space to bring up its system menu, then M to select Move, then I hold the Up arrow until the window is brought up. The top of the new window is a ways below the bottom of the screen. I have to hold down the Up arrow for a second or two before it appears.
I just put together a little AutoHotKey script that shows the position of the active window. When I drop the tab at the very top of either screen, the Y position of the new window will be about 1265. If I drop it lower on the screen, the offset seems to be about the same. I just dropped it at the very bottom of my screen, giving a Y coordinate of 2346, which minus 1080 is 1266.
Dropping it at the bottom of my second monitor gives a Y position of 2165, minus 900 is 1265.
I don't know what that 1265 number comes from but hopefully this helps you find it.