Changing numbers of products / refresh at checkout

Hi
I am new to HikaShop and so far I find it a nice tool, indeed a lot easier than Virtuemart.

Now I found a strange behaviour: If I change the number of ordered products on the checkout page and click the refresh button (or use the enter key), below the total money amount disappears and what's worse the shipping costs are no longer listed and and added to the total. That means, if someone changes the amount of products in this stage of the checkout process, the shipping costs are not included and he will be able to proceed to PayPal.

Any help is highly appreciated.
Thank you and greetings from Switzerland
Michael

You'll find the shop I am working on here:
www.foto.schmizz.ch/index.php/de/fotoshop

Thank you so much for your help - at 02:40 in the morning

I'll just check it out.
Best regards, and again, thanks a lot.