When RadButton (ButtonType="StandardButton") is set with a particular width, the text of the button is decentralized. Fix the center of this text. For the time being can be used either the new SkinnedButton or the following workaround:

    <style type="text/css">
        .rbDecorated
        {
            padding-left: 6px !important;
            padding-right: 10px !important;
        }
    </style>