If you create a grouping view for a grid, and enable the grouping display, the group is not rendered for the region that you have to scroll to (see screenshot).

I provide a patch file against your explorer code to reproduce. I changed entry point to go straight to this example, since explorer framework was making it difficult for me to create a scrolling grid.

Once pages loads, expand the "Change Column" as far as you can. Then expand the "Price" Column, this will force the scroll bar to render.

GroupingViewRenderingNotExtendedIfScrollbar.jpg

Code:
Index: src/main/java/com/sencha/gxt/explorer/Explorer.gwt.xml
===================================================================
--- src/main/java/com/sencha/gxt/explorer/Explorer.gwt.xml	(revision 2134)
+++ src/main/java/com/sencha/gxt/explorer/Explorer.gwt.xml	(working copy)
@@ -12,7 +12,7 @@
 
 <!--   <set-property name="gxt.logging.enabled" value="true" /> -->
 
-  <inherits name="com.sencha.gwt.uibinder.UiBinder" />
+  <!-- <inherits name="com.sencha.gwt.uibinder.UiBinder" />  -->
 
   <!-- Specify the paths for translatable code -->
   <source path='client' />
@@ -31,5 +31,6 @@
 
   <set-configuration-property name="GXT.state.autoBeanFactory" value="com.sencha.gxt.explorer.client.misc.WindowStateExample.ExampleAutoBeanFactory" />
 
-  <entry-point class='com.sencha.gxt.explorer.client.Explorer' />
+  <!-- <entry-point class='com.sencha.gxt.explorer.client.Explorer' /> -->
+  <entry-point class='com.sencha.gxt.explorer.client.grid.GroupingGridExample'/>
 </module>
Index: src/main/java/com/sencha/gxt/explorer/client/grid/GroupingGridExample.java
===================================================================
--- src/main/java/com/sencha/gxt/explorer/client/grid/GroupingGridExample.java	(revision 2134)
+++ src/main/java/com/sencha/gxt/explorer/client/grid/GroupingGridExample.java	(working copy)
@@ -21,12 +21,13 @@
 import com.sencha.gxt.examples.resources.client.model.Stock;
 import com.sencha.gxt.explorer.client.model.Example.Detail;
 import com.sencha.gxt.widget.core.client.ContentPanel;
+import com.sencha.gxt.widget.core.client.container.Viewport;
 import com.sencha.gxt.widget.core.client.grid.ColumnConfig;
 import com.sencha.gxt.widget.core.client.grid.ColumnModel;
 import com.sencha.gxt.widget.core.client.grid.Grid;
 import com.sencha.gxt.widget.core.client.grid.GroupingView;
 
-@Detail(name = "Grouping Grid", icon = "grouping", category = "Grid", classes = {Stock.class})
+@Detail(name = "Grouping Grid", icon = "grouping", category = "Grid", classes = {Stock.class}, fit=true)
 public class GroupingGridExample implements EntryPoint, IsWidget {
   
   interface StockProperties extends PropertyAccess<Stock> {
@@ -75,7 +76,7 @@
 
     final GroupingView<Stock> view = new GroupingView<Stock>();
     view.setShowGroupedColumn(false);
-    view.setForceFit(true);
+   // view.setForceFit(true);
 
     Grid<Stock> grid = new Grid<Stock>(store, cm);
     grid.setView(view);
@@ -97,7 +98,9 @@
 
   @Override
   public void onModuleLoad() {
-    RootPanel.get().add(this);
+	  Viewport vp = new Viewport();
+	  vp.setWidget(this);
+    RootPanel.get().add(vp);
   }
 
 }