form parameter autop

Hi, I encounter a strange autop formatting in a dynamically populated field (normal paragraph text field, not html), can you help me find out why ?

here is my parameter code , the output is visible here

http://dev.prairie-fleurie.com/partager/produit/598-509-466

add_filter("gform_autoresponder_email_4", "poleouest_change_notification_email_4", 10, 2);
  function poleouest_change_notification_email_4()
  {
      $dest =  $_POST["input_2"] ;
      if ($_POST["input_3"])      $dest .=  "," . $_POST["input_3"];
      if ($_POST["input_4"])      $dest .=  "," . $_POST["input_4"];
      if ($_POST["input_5"])      $dest .=  "," . $_POST["input_5"];
      if ($_POST["input_6"])      $dest .=  "," . $_POST["input_6"];
      return $dest;
  }
  //http://www.gravityhelp.com/documentation/page/Gform_field_value_$parameter_name
  add_filter("gform_field_value_messagepartage", "populate_message");
    function populate_message($value){
        $str= "Bonjour, 

        je souhaite vous faire partager le site ffff.com à cette adresse: 

         ";
        if (strstr( $_SERVER["HTTP_REFERER"], " ffff.com"))
        $str .=  $_SERVER["HTTP_REFERER"];
        else $str .= "http://www.ffff.com.com";
       if (get_query_var("produit")!="")
           $str .=  "/produit/" . get_query_var("produit");
        return $str.$value;
    }