Dynamically change the CommandBarButton.Picture. (Vs2010 isolated shell))

Hi,  

    I want to change image of CommandBarButton dynamically, the code is as following:

  CommandBarButton rmdCommandBarButton = GetRmdCommandButton();
            var picture = GetPicOfRmdCommandButton();
            if (rmdCommandBarButton != null && picture != null && rmdCommandBarButton.Picture != picture)
                rmdCommandBarButton.Picture = (StdPicture) picture;

When i call  the   "rmdCommandBarButton.Picture = (StdPicture) picture",The button icon in the toolbar work well, but  in the menu  item of Add or Remove Button,  the icon cannot display 

Why?