Shopping Cart problem after upgrade - SEO URL

I upgraded from 1.3.8 to 1.3.9h and now the shopping cart is causing problems.

When i add a product from a product listing page - http://www.fashionamour.com.au/bohemian-silk-dresses-c-153.html
and click "continue shopping" it takes me back to the previous page, which is correct.
But if i then add another product from that page, the shopping cart adds to the quantity of the original product when it should have added the new product to the cart.

If i go from the cart to the same page http://www.fashionamour.com.au/bohemian-silk-dresses-c-153.html
via the category link and add a new product, the cart works like it should and new product is added.

Hope that makes sense... help!!

What happens if you disable your url rewrite?

What happens if you switch to the classic template?

Sorry, I forgot to mention, i tested in classic template, same problem. I'll try the SEO re-writes now.
Thanks

Thanks Kobra, turning off SEO URLs fixed the problem. I'll try updating the SEO URLs. Is there anything else I should look at?

I've updated SEO URLs but it didnt fix the "continue shopping" link problem.

I've updated SEO URLs but it didnt fix the "continue shopping" link problem.
I do not recommend nor use any of these as they all have issues

Might post in their support thread

Now my home page text is missing. I'm not sure if it's related to upgrading the SEO URLs but the home page only shows the featured and specials products now. I checked in admin > define pages and the text is till there for the home page. I switched to clessic template but that didn't fix it.