I have the same problem in IE and Firefox.
I have the same problem in IE and Firefox. I have commented out the line you have suggested and the problem with the script jumping to the top of the page is fixed.
However, the screen does not scroll up or down when I drag the image either above the first visible row or below the last visible row.
The only was to get it to scroll up or down is by using the scroll button while holding the left mouse button down.