We have a RadBook control defined as:
<telerik:RadBook Margin="20" Height="400" x:Name="book" IsKeyboardNavigationEnabled="True">
<telerik:RadBookItem Content="Page1" />
<telerik:RadBookItem Content="Page2" />
<telerik:RadBookItem Content="Page3" />
</telerik:RadBook>

If we go to the last (third) page, the RightPageIndex becomes 2, and after that go back to the Page1 and Page2, the RightPageIndex is 0, which is incorrect.
The issue manifests itself ONLY if the keyboard is used for navigation. If pages are turned with the mouse - the RightPageIndex is correct.