Scroll Bar anomalies

I'm not really sure what causes this, but sometimes, I can scroll way further down than I really should. This applies to just about everywhere on this website: the forums, the comments section of each game, and even the drawing canvas.

Not really sure how long has this been going on, but I have noticed it in some of the videos I've done, such as this one:

http://www.youtube.com/watch?v=E4pKu_VsNzw&feature=BFa&list=PLC5D49536E4F30F95

Ignore the drawing and pay attention to the scroll bar on the right for just the moment. It's quite bizarre.