Today, when everything was fine yesterday, any program I run that has a List auto scrolls the list to the bottom and I can't access the other items

Has anyone ever heard of that happening before? Windows 7 - 64.
Edit - not just programs written in PB. I just navigated to Windows 'Programs and Features' and it's List is the same - scrolls to the bottom, if you try to scroll up, it just scrolls back down again - like being pulled by gravity.