Grid Utils SimpleStringConverter

I am havign a problem when using the EditButtonValueRenderer also the Simple String Converter

grid.getColumn("username")
            .setRenderer(new EditButtonValueRenderer(new RendererClickListener() {

                @Override
                public void click(RendererClickEvent event) {
                    // TODO Auto-generated method stub
                    System.out.println("Change Privilege" + event.getPropertyId());
                }
            }), new SimpleStringConverter<String>(String.class) {

                @Override
                public String convertToPresentation(String value, Class<? extends String> targetType, Locale locale)
                        throws com.vaadin.data.util.converter.Converter.ConversionException {
                    // TODO Auto-generated method stub
                    return String.format("<b>%s</b>", value);
                }
            });

The column username is came from

GeneratedPropertyContainer

which means the username is came from the child value of the main class value
I use JPAContainer to put data on the grid..
when I run the application the grid is on the mess.

how do I solve this?