meta box & callback function

Using classes like you are, your callback function is implemented wrong:

add_meta_box( 
             'post_format_box'
            ,__( 'Post Format Content', self::LANG )
            ,@$this->render()
            ,'post' 
            ,'advanced'
            ,'high'
        );

Should be:

add_meta_box( 
             'post_format_box'
            ,__( 'Post Format Content', self::LANG )
            ,array($this, 'render')
            ,'post' 
            ,'advanced'
            ,'high'
        );