We noticed that chapters in Books that include wide content (e.g., two images side by side, each in their own table cell), there are no horizontal scroll bars. If the browser window is narrowed to the point where you can't see both images, a horizontal scroll does not appear. It's therefore impossible to view the entire chapter unless you expand the browser (in Moodle 1.9.18, for the same chapter, we do see the horizontal scroll bar). Also, this same content, when placed in a Page, a horizontal scroll bar is present. I have attached two images to demonstrate this... one showing the book chapter (with no scroll bar), and the other showing the same content in a page (with a scroll bar). We see this on any stock theme, and all browsers.