Wish I could offer some advise. but I cant say I've seen this since sonar X3 and earlier.
It could be your mouse causing the issue. or possibly a controller taking focus on the scroll wheel.
Have you tried another mouse ? I've had issues with Logitech mice myself.
Im not sure if this helps but when you are all the way to the top again, you can hit the Up arrow to bring you all the way to the bottom again (rather than scrolling through mounds of tracks).
Try going to track 1 and hit the up arrow, you'll see what I mean.