Michael, are you flicking the pan in a direction or holding down the mouse and panning around? There's a delay at first when you first click the mouse to start a pan. I've found that when I'm flicking, the map doesn't really start moving until after I've depressed the mouse as it catches up with the command. If I click and hold the mouse, so my map is moving around relatively in real time, after I let go, the map stays put.
