Hi,
Then why do you suspect HikaShop if you've configured it the same as the other website and that the problem is on the payment page of the payment gateway ?
I can only tell you what I already told you because that's the solution to the problem you have:
That behavior comes from the settings of your PayPal merchant account. So you need to change it there.
www.paypal.com/cgi-bin/webscr?cmd=p/mer/...turn_summary-outside
Please contact the PayPal support regarding this option. If it's not like in the PayPal documentation, they should be able to tell you what to do.
I'm afraid I can't help further on that issue.