Extract from GWT-EXT Java Doc
public class FitLayoutextends ContainerLayout
This is a base class for layouts that contain a single item that automatically expands to fill the layout's container.
FitLayout does not have any direct config options (other than inherited ones). To fit a panel to a container using FitLayout, simply set layout to FitLayout on the container and add a single panel to it. If the container has multiple panels, only the first one will be displayed.My experience is, if you did not conform to this criteria, your remaining layout within the FitLayout panel will go crazy (Especially, grid component)