Overview page in backend does not show column values

I’m trying to make the overview page for my custom page type, but I can not get WP to display the custom field values, even though it’s possible to print the column headings.
I have defined the custom fields in the functions.php and in the individual pages they are also displayed correctly:

add_action("admin_init","cpt_workshop_meta_boxen");
 add_action('save_post','cpt_workshop_daten_speichern');
 
 function cpt_workshop_meta_boxen(){
	add_meta_box("art-meta", "Workshopart","cpt_workshop_feld_art", "workshopseite","normal","default");
	add_meta_box("datum-meta", "Datum","cpt_workshop_feld_datum", "workshopseite","normal","default");
	add_meta_box("ort-meta", "Ort","cpt_workshop_feld_ort", "workshopseite","normal","default");
	add_meta_box("leitung-meta", "Leitung","cpt_workshop_feld_leitung", "workshopseite","normal","default");
 }
 
 function cpt_workshop_feld_art(){
	global $post;
	$custom = get_post_custom($post->ID);
	$art = $custom["art"][0];
	echo '<input name="art" value="' . $art . '" />';
 }
  function cpt_workshop_feld_datum(){
	global $post;
	$custom = get_post_custom($post->ID);
	$datum = $custom["datum"][0];
	echo '<input name="datum" value="' . $datum . '" />';
 }
  function cpt_workshop_feld_ort(){
	global $post;
	$custom = get_post_custom($post->ID);
	$ort = $custom["ort"][0];
	echo '<input name="ort" value="' . $ort . '" />';
 }
   function cpt_workshop_feld_leitung(){
	global $post;
	$custom = get_post_custom($post->ID);
	$leitung = $custom["leitung"][0];
	echo '<input name="leitung" value="' . $leitung . '" />';
 }
   
 function cpt_workshop_daten_speichern (){
	global $post;
	update_post_meta($post->ID, "art", $_POST["art"]);
	update_post_meta($post->ID, "datum", $_POST["datum"]);
	update_post_meta($post->ID, "ort", $_POST["ort"]);
	update_post_meta($post->ID, "leitung", $_POST["leitung"]);
 }

In the overview page, I just do not get the values displayed. The code in the functions.php:

add_filter("manage_edit-workshopseite_columns", 
   "cpt_workshopseite_spalten");
   add_action("manage_posts_custom_column",  
   "cpt_workshopseite_neue_spalte");

   function cpt_workshopseite_spalten($columns){
      $columns = array(
                 "cb" => "<input type=\"checkbox\" />",
                 "title" => "Workshoptitel",
		 "datum" => "Datum",
                 "ort" => "Ort",
                 "date" => "Hinzugefügt"
      );
	
      return $columns;
   }

   function cpt_workshopseite_neue_spalte($column){
      global $post;
      if ("datum" == $column) {
         $custom = get_post_custom();
         echo $custom["datum"][0];
      }
		
      elseif ("ort" == $column) {
         $custom = get_post_custom();
         echo $custom["ort"][0];
      }
   }

What am I doing wrong ?
??
Brgds
Worels

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