This is as utterly bizarre as it sounds. I solved it by re-booting. I was in the blender python editor, (I had left the computer idle for a while), and when I come back, the file I have open suddenly scrolls to it's top, and "jumps around" when I try to scroll back down. I close blender hoping that will solve the problem. The file system is the next window on top. -it- scrolls to it's top. I close everything. I open the applications tab to re-start blender: -it- scrolls to it's top. ie, if I select one of the items on the list, I think this works by the mouse just being over it, it doesn't remain high-lighted.. I can't quite remember what it did, but I think it started switching back and fourth between the one that should be active and the top one, or switched to the one that should be active whenever this changed, then went back to the top.