I think I might have found a bug? With a clean install of zen cart 1.3.0.1.
I've noticed with my settings I end up with incorrect URL's on the product listing page, it's showing an extra product_id parameter. And it is conflicting with my other mods because they're expecting the product_id parameter to be in the URL only once.

Admin settings:

My store
Display Cart After Adding Product = false

Product listings
Display Multiple Products Qty Box Status and Set Button Location = 0


After adding a new item to cart by clicking on "buy now" button on product listing page you're redirected back to the same page you where on when you clicked buy now button, but the urls of all the other buy now buttons has the parameter "product_id" in it twice. This extra "product_id" seems to come from the function zen_get_all_get_params which builds the redirct URL, I think what's happening is that the this function is throwing the product_id back into the url, and then the product_id outside of the fuction is added in a second time to build the url, it seems to be throwing off my Ultimate SEO URLs mod, and I think it even was flaking out even without the mods too, if you'd click on another buy now button the same page again you'd end up with multiple quantities of the first item you selected. I get a headache looking at the zen cart functions and trying to fix them so I'm just going to make my own get all parameter's function and use that for this situation, unless someone has a better easier idea?