CanvasItem can't render disabled state normally

[garywu]

GWT version: 2.0.4
SmartGWT version: 2.2

form items in dynamic form "innerForm" that embedded in a canvas item can not render gray background after disabled

final VStack pane = new VStack();

Button b = new Button("Disable");
b.addClickHandler(new ClickHandler() {
    public void onClick(ClickEvent event) {
        pane.disable();
    }
});
pane.addMember(b);


DynamicForm form = new DynamicForm();

DynamicForm innerForm = new DynamicForm();
TextItem f1 = new TextItem();
ButtonItem f2 = new ButtonItem();
SelectItem f3 = new SelectItem();
innerForm.setFields(f1, f2, f3);

CanvasItem ci = new CanvasItem();
ci.setCanvas(innerForm);
form.setFields(ci);

pane.addMember(form);

pane.draw();