Hi,
I just tried to reproduce the issue on my local, latest Joomla 2.5.28 version and latest HikaShop verions (2.6.1).
It is working as expected, even when using different settings for the action after we add a product to the cart.
So could you give us a link to a page with the issue in order to test on your site to have more clues ?
We will potentially need a backend access and FTP to your website. (info can be sent via our contact form with a link to that topic in your message).
www.hikashop.com/support/contact-us.html