The remote that comes with the 3930 is an IR remote, so it has to be pointed at the front of the Express (you probably already know that). I can think of a couple of possibilities - there's a stuck button on the remote or there's some kind of interference (like bright sunlight). You can use a digital camera like the one in your phone to check for stuck buttons. Point the remote at the camera and press a button and you should see a flash of light on the screen. If it's a continuous light or a constant flashing then a button is stuck. Try repositioning the Express if there's any bright light hitting it.
I saw this scrolling problem myself once, but I can't repeat it. As I recall, just moving myself and/or the Roku made it stop.
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