I have a problem in my Sencha Touch application (I'm working with Sencha Architect 2.1.0)

I have a Container (Ext.Container) which contains a NestedList (Ext.dataview.NestedList). My Container is configured with a "Fit" layout. My nestedList is filled with a Treestore. When I navigate in my nestedlist to go to the leaf node, everything looks fine but when I scroll on the last node (leaf), and I go back to the root level, everything dissapears ! When I don't scroll, everything is fine. Why ?

Did I affect the wrong layout to my container ? I did not set any height, is it an error ? I replace my Container with a Panel (Ext.Panel) and I have the same result.