为什么jquery-ui自动完成列表不会显示在大型列表中

Question

在较小的选项列表中，自动完成下拉列表确实显示焦点。但如果选项超过特定数字（确切地说是50），则不再显示。

无论列表中的选项数量是多少，如何显示？

$(document).ready(function() {
  var sst;
  //auto complete for artist
  $('#artist').autocomplete({
    source: 'artists.php',
    minLength: 0,
    select: function(a, b) {
      sst = b.item.value;
    }
  }).focus(function() {
    $(this).data("uiAutocomplete").search($(this).val());
  });
  //auto complete for title
  $('#title').autocomplete({
    source: function(request, response) {
      $.ajax({
        url: "titles.php",
        dataType: "json",
        data: {
          q1: sst,
          q2: request.term
        },
        success: function(data) {
          response(data);
        }
      });
    },
    minLength: 0
  }).on('focus', function(event) {
    $(this).autocomplete("search", "");
  });
});

mysql查询：

      <?php 
$db = mysql_connect('localhost','root','1313');
if(!$db){
        die( "connection failed  ");
}
$db_s = mysql_select_db("LYRICSFINDER",$db);
$data = array();
$searchTerm1 = trim(strip_tags($_GET["q1"]));
$searchTerm1 = addslashes($searchTerm1); 
$searchTerm2 = trim(strip_tags($_GET["q2"]));
$searchTerm2 = addslashes($searchTerm2);      
$query = "SELECT TITLE FROM DATA WHERE ARTIST LIKE '%".$searchTerm1."%' AND TITLE  LIKE '%".$searchTerm2."%' ORDER BY TITLE ASC";
$result = mysql_query($query,$db);
$i=0;
while($row = mysql_fetch_assoc($result) ){
    $data[] = $row['TITLE'];
    $i++;
    if($i>50)break;
}
mysql_close($db);
echo json_encode($data);
  ?>