I'm having the same problem witn Microsoft Word 2010 when using a mouse to scroll/modify text.
When using my previous version of word, when I wanted to scroll to a partilular line and modify something, I could page down, or I could move down by pointing at the down arrow and dragging the mouse pointer down through the document, or click and hold the left button and move the pointer up or down to wherever I want to modify something. When I got to where wanted to be, I could move the pointer around the screen to the start of an area I wanted to delete/change/whatever, click on and drag to highlight what I want to modify, and delete, edit, or whatever I want to do.
With MS word 2010, first of all the scrolling action is jerky, and sometime it goes off and scrolls down on its own with nothing clicked on the mouse.
With 2010, when I scroll to find what I want to edit, as soon as I move the pointer off the thumbwheel and try to move left to select something to change, the window arbitrarily and uncontrollably jumps to somewhere else in the document.