Go into Setting > Activator and check to see what the "Shake" setting has been assigned to. If it's "Respring" then uncheck it. If not: Try a reset. Close all apps then - Hold down the HOME, bottom button, and the SLEEP, top button, for about 10 seconds until the Apple icon appears, then release buttons. Allow it to reboot, it may take a few minutes, don't panic like I did, wait for it to reboot. Cures many weird problems on iOS devices.