ApplicationButton and QuickStartToolbar layout do not look good when user changed the theme in runtime.
Issue can be reproduced with Office2010Silver, Deser, HighContrastBlack and Windows7 themes.

Workaround:
 call recursively the UpdateLayout method for all RadControls in the form:

ThemeResolutionService.ApplicationThemeName = item.Text;
    this.RefreshAll();
    m_strThemeName = item.Text;
    SaveThemeName();
...
}
 
private void RefreshAll()
{
    foreach(Control control in this.Controls)
    {
        RefreshAllControls(control);
    }
}
 
void RefreshAllControls(Control ctrl)
{
    foreach (Control control in ctrl.Controls)
    {
        RadControl radControl = control as RadControl;
        if (radControl != null)
        {
            radControl.RootElement.InvalidateMeasure(true);
            radControl.RootElement.UpdateLayout();                   
        }
        RefreshAllControls(control);
    }
}