ajax +upload 詭異的現象？

<code><form method="post" name="form" id="form" enctype="multipart/form-data">
              <textarea name="post" rows="3" maxlength="100" id="post"></textarea>
                 
                  <input type="file" name="myFile">
                 
                          <button type="submit" id="post_btn">發佈</button> <span id="show"></span>
              </form>
              
$("#post_btn").click(function(e){
     e.preventDefault();

        if (post.value=='')
        {
            post.focus();
            document.getElementById("show").innerHTML = "勿為空";
            return (false);
        }
        else
        {
            var timelinedata = new FormData($("#form")[0]);
            
            $.ajax({
                type:"POST",
                url:"ing",
                data: timelinedata,
                cache: false,
                contentType: false,
                processData: false,
                success:function(data){
                    $("#show").html(data);
                }
            });
        }
    
});</code>

<code>$post = htmlspecialchars(preg_replace("/[\'\"]+/" , '' ,$_POST['post']),ENT_QUOTES);
$addtime = time();
          
$SQL_RE = mysql_query("SELECT * FROM `xxx`
WHERE `post` = '".$post."'
");    

if(mysql_num_rows($SQL_RE)==0)
{
        $allowTime = 60; 
        $allowT = md5();
      if (time() - $_SESSION[$allowT] > $allowTime)
      {
          $_SESSION[$allowT] = time(); 
          
          $sql = mysql_query("INSERT INTO `xxx`
          (`post`,`id`,`addtime`)
          VALUES
          ('".$post."','".$_SESSION['userid']."','".$addtime."') 
              ");

          echo '已發佈';
      }
      else
      {
          echo '過於頻繁，請稍候';
          
      
      }
}
else
{
    echo '你發佈了相同的內容';
}</code>

<code><form method="post" name="form" id="form" enctype="multipart/form-data">
              <textarea name="post" rows="3" maxlength="100" id="post"></textarea>
                 
                  <input type="file" name="myFile">
                 
                          <button type="submit" id="post_btn">發佈</button> <span id="show"></span>
              </form>
              
$("#post_btn").click(function(e){
     e.preventDefault();

        if (post.value=='')
        {
            post.focus();
            document.getElementById("show").innerHTML = "勿為空";
            return (false);
        }
        else
        {
            var timelinedata = new FormData($("#form")[0]);
            
            $.ajax({
                type:"POST",
                url:"ing",
                data: timelinedata,
                cache: false,
                contentType: false,
                processData: false,
                success:function(data){
                    $("#show").html(data);
                }
            });
        }
    
});</code>

<code>$post = htmlspecialchars(preg_replace("/[\'\"]+/" , '' ,$_POST['post']),ENT_QUOTES);
$addtime = time();
          
$SQL_RE = mysql_query("SELECT * FROM `xxx`
WHERE `post` = '".$post."'
");    

if(mysql_num_rows($SQL_RE)==0)
{
        $allowTime = 60; 
        $allowT = md5();
      if (time() - $_SESSION[$allowT] > $allowTime)
      {
          $_SESSION[$allowT] = time(); 
          
          $sql = mysql_query("INSERT INTO `xxx`
          (`post`,`id`,`addtime`)
          VALUES
          ('".$post."','".$_SESSION['userid']."','".$addtime."') 
              ");

          echo '已發佈';
      }
      else
      {
          echo '過於頻繁，請稍候';
          
      
      }
}
else
{
    echo '你發佈了相同的內容';
}</code>