[ic] Reloading Checkout page adds new item

[Interchange User]

In my Checkout page, when I reload that page, a new item (equivalent 
to the last item added) will be added to my order.  Any ideas what 
the cause could be? I suspected it was due to some mv_order_* used.  
But I only have these 3 mv_order_* :

<INPUT TYPE=hidden NAME=mv_order_profile VALUE=my_checkout_profile>
<INPUT TYPE=hidden NAME=mv_order_receipt VALUE="ord/wp_redirect">
<INPUT TYPE=hidden NAME=mv_order_route 
VALUE="[either]__ORDER_ROUTES__[or]log[/either]">

Any clues?  Let me know if you need more program codes before you can 
help me.  But off-hand, does anyone know why this is so?