ทำไม php insert ข้อมูลลง database สองรอบ (เมื่อใช้ browser chrome 12 ใช้ ie ff ไม่เป็นไร)

<?php
session_start();
include("common/connect.php");
include("common/fncAll.php");
echo '<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />';


$quiz_topic= $_POST['quiz_topic'];
$quiz_message = $_POST['quiz_message'];
$quiz_name = $_POST['quiz_name'];
$quiz_email = $_POST['quiz_email'];
$quiz_date  = date('Y-m-d h:i:s');
$quiz_attach =$_FILES['quiz_attach']; //array
/*
echo $quiz_attach[name] ;  
echo $quiz_attach[type] ;   
echo $quiz_attach[tmp_name] ;
echo $quiz_attach[size] ;
*/

 
//print_r($quiz_attach ) ; exit();

/////////////////// get extention  for  attach file //////////////////////
$extention = explode( '/' , $quiz_attach[type] ); //array
//print_r($extention) ;
//exit();
 
if ($quiz_topic =='' || $quiz_message =='' || $quiz_name =='' || $quiz_email =='' || $quiz_date ==''  ){  
	echo  '<script>alert("คุณกรอกข้อมูลไม่ครบ");</script>';
	echo '<script>history.back()</script>';	
} 

if($quiz_attach[size]>0  ){

		  if (  $quiz_attach[type] == "image/jpeg" ||  $quiz_attach[type] ==  "image/pjpeg" ||  $quiz_attach[type] == "image/gif" ){
		  
				  $name_from_time=time();  // create new name for photo upload
				  $newname =  $name_from_time.".".$extention[1]; 
				 // echo $newname; exit();
				  
				  move_uploaded_file($quiz_attach[tmp_name], "attach/$newname"  );
				  
				    $sql = "insert into  tb_quiz  ( id_quiz , quiz_topic , quiz_message , quiz_name , quiz_email ,  quiz_attach, quiz_date, quiz_view, quiz_reply ) "  ;
					$sql .= "value ( '' , '$quiz_topic ', '$quiz_message',  '$quiz_name',  '$quiz_email',  '$newname',  '$quiz_date','' ,'' ) "  ; 
					 echo $sql ; exit();
					
					$result =mysql_query($sql, $link);
					//print_r($result);
								
							if (! ($result) ){
							echo  '<script>	alert("ไม่สามารถเพิ่มกระทู้ได้ครับ");</script>'; 
							echo	 '<script>	history.back();</script>	';
							
							}else{	
							echo  '<script>	alert("เพิ่มกระทู้แล้วครับ");</script>'; 	 
							echo	 '<script>window.location="index.php"</script>	';	
							}
				
		   
		 }else{	
			  echo '<script>alert ("ภาพที่อัพโหลดต้องเป็นนามสกุล JPG หรือ GIF เท่านั้น")</script>';	
			  echo '<script>history.back()</script>';	
		 }

 
}else{
 
     $sql = "insert into  tb_quiz  ( id_quiz , quiz_topic , quiz_message , quiz_name , quiz_email ,  quiz_attach, quiz_date, quiz_view, quiz_reply ) "  ;
					$sql .= "value ( '' , '$quiz_topic ', '$quiz_message',  '$quiz_name',  '$quiz_email',  '',  '$quiz_date','' ,'' ) "  ; 
					 //echo $sql ;
					//exit();
					
					$result =mysql_query($sql, $link);
					//print_r($result);
								
							if (! ($result) ){
							echo  '<script>	alert("ไม่สามารถเพิ่มกระทู้ได้ครับ");</script>'; 
							echo	 '<script>	history.back();</script>	';
							
							}else{	
							echo  '<script>	alert("เพิ่มกระทู้แล้วครับ");</script>'; 	 
							echo	 '<script>window.location="index.php"</script>	';	
							}
}

 	 
?>