A LayoutPanel inside a ScrollPanel does not work and really does not make that much sense. The parent of a LayoutPanel needs a size otherwise LayoutPanel does not work. On the other hand a ScrollPanel has an inner scrollable element that can not have any specific size as it must adapt to its child size. Otherwise ScrollPanel can not show scroll bars.
Normally you would have ScrollPanels inside center and maybe inside east/west. DockLayoutPanel should be used to layout the very basic areas of a
web application and a web application typically has fixed header/footer/sidebars and a scrollable center area. You dont want to scroll the entire web application, only its content.
If you need a more website like layout with vertical/horizontal scrollbars that scroll the whole website you better not use LayoutPanels.
-- J.