facebook application - everything is posted twice - iframe-based application

I am building an iframe based - facebook application. My problem is, whenever I redirect user to any page, I can see pages are loaded twice. (first, it shows the page without css and then again page is loaded with css). Same is happening when I post any form.

So, every form is posted twice. Data is added twice for each and every action. Moreover, I can see all my POST data in url... facebook is passing all session data in URL. Is it normal?

Am I missing something? Please help me. Below is my code.

foreach($records as $product_list)
{
?>
  <tr>
    <td width="250">
      <form name="frm_product_<?php echo $product_list->product_id;  ?>" id="frm_product_<?php echo $product_list-> product_id;  ?>" action="cart.php">
      <?php echo $product_list->product_name; ?><br />
      Price : <?php echo $product_list->price; ?>&nbsp;SGD<br />
      <input type="hidden" name="product_id" value="<?php  echo $product_list->product_id; ?>" />
      <input type="submit" name="btn_submit_<?php  echo $product_list->product_id; ?>" id="btn_submit_<?php  echo $product_list->product_id; ?>" value="Add to Cart" />
      <input type="hidden" name="action" value="add" />
      </form>
    </td>
  </tr>
  <tr>
    <td>&nbsp;</开发者_C百科td>
  </tr>
<?php
}
?>

if(isset($_REQUEST['action']) && $_REQUEST['action']=='add')
{

  $cart = new Cart($db);
  $cart->user_id = 1;
  $cart->product_id = $_REQUEST['product_id'];
  $cart->qty = 1;   
  $cart->add_to_cart1();  //this is adding items two times
}

Thanks in advance.

For double post problems always check you do not have somewhere an image href set to '' (empty string). It colud be an or an url() in a css. This is not an issue but a design decision in HTTP, empty GET url (like an empty image src) means redio the request that get you on the page (that could be a POST). It's maybe not your case, but last time I was it by that it took me 3 days to find :-)