Clicking on scroll bar goes more than one page

I'm reviewing a gc.log that is approximately 12 hours long.  My window is sized such that I can see 20m without scrolling.

If I click in the space on the horizontal scroll bar, it should go one 'page'.  So if I'm on a page showing 6h to 6h20m, and click in the scroll bar to move it right, it should show roughly 6h20m to 6h40.  Instead, it moves to 7h20 to 7h40.
