Hi,
When you have the page with the paypal button, the order is already created so it is already "too late".
If you re-submit the same form going back in the history, you will re-submit the old order which has already been send to paypal (so it won't accept it).
It is not another order, it is just that you try to re-pay something that you have already submitted and paid.
About the empty cart, you have an option in HikaShop so you can say when you want HikaShop to empty the cart.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.