1. On the top right corner of the upper WebHelp pane, there are 2 or 3 buttons depending on whether you are on the first page (Sidebar | Next), the last page (Sidebar | Prev) or on another page (Sidebar | Prev | Next). There should always be 3 buttons, grayed out if needed, instead of having the size of that area change depending on context. It's generally a bad design idea to change the size of an area and the options presented to the user depending on the context, plus it's visually annoying.
2. Another thing that we should add to the next/previous/up buttons: When you mouse over a button, it should show a tool tip containing the title of the next chunk.