You're right, this is a bug, part of the code in that function is missing, it should be like this:

private FrameworkElement FindStateGroup(FrameworkElement context)

{

if (context != null)

{

FrameworkElement current = context;

FrameworkElement parent = context.Parent;

    while (!HasStateGroup(current) && ShouldWalkTree(parent))
    {
        current = parent;
        parent = parent.Parent;
    }

    if (HasStateGroup(current))
    {
        FrameworkElement templatedParent = current.TemplatedParent;
        if (templatedParent != null && templatedParent is Control)
        {
            return templatedParent;
        }
        if (parent != null && parent is UserControl)
        {
            return parent;
        }

        return current;
    }
}

return null;
}