Hi,
I would like to report that I am seeing this also. I just upgraded to 3.87, and both pages refer to each other, but I get "No ProductID Exists" when clicking a product in the cart. The site is not live yet... but we are trying to make it live soon.
The url when you click on the image or text link in the BuyNow module simply goes to a ProductDetails.aspx page, with no form data. But, the Add to Cart function does work with the Add to Cart button. The Continue Shopping button works correctly also, so both entries are pointing to each other.
So, when you click on a product link or image in the BuyNow module, you just get the following: