My wireless mouse (Microsoft Wireless Mobile Mouse 4000 on Windows 7) has started acting this way: When you press the middle button in a browser (expecting a link to open in a new tab) it will instead act like if you've pressed Alt+Tab, bringing up the windows with application icons for a a few seconds and then going into a random open application.
The wheel button in Control Panel's Mouse options is set to "Flip" (default). Restoring defaults and restarting the computer hasn't helped.
