I just wasted a few days trying to track down a non existent bug.
I couldn't work out why the scroll bar calculations were incorrect for the page size. Then i finally remembered i made it so that if you add a sprite to a page, then the page resizes to fit the sprite if the page is too small. This is so pages can grow at runtime if the page content is updated.
There is now another option to set this per sprite, so you can decide which sprites effect page size.
I also added the option to have scrollbar thumbs dynamically resize with a tween motion, and the option to hide scrollbars when the page is smaller than the window area.