[Not a Bug] Product Page - Add To Cart, Reviews, Odd Behavior

[k1ra]

I am running Zencart 1.5.1.
Upgraded from 1.3.9 using official upgrade procedure.
PHP 5.4.24

Plugins installed:

• Ask A Question
• Flexible Product Listing
• Image Handler 4
• Multi-Cross Sell
• Stock By Attributes
• CSS3 Buttons by lat9

Other:
Jquery UI 1.10.4.

I have a display only attribute set to force user selection of product attribute [Size]. Whilst playing with Jquery UI to style the radio buttons and CSS buttons, I discovered something odd:

1. I hit Add To Cart without selecting a size, I get the proper error message.
2. I hit the Go To Reviews Page button, and it sends me to a page that says 'Sorry, Product not found'
3. I hit the browser back button, and see the green message 'Successfully added product to cart' [there is nothing in the cart]
4. I hit the Go To Reviews Page button again, and it sends me to the proper page.

I disabled Jquery UI. I could still reproduce this behavior.
I switched to Default Template. I could still reproduce this behavior, with one exception:
hitting the browser back button [step #3 above] gave me a 'Document Expired. This document is no longer available.' browser message.

I can also verify that refreshing the page after receiving the error in step #1, or hitting another link and then hitting the browser back button, will reproduce the 'Successfully added product to cart' message OR the 'Document Expired' message, depending on the template.

[mc12345678]

If I may ask, is the product type that is presenting this problem something other than a standard product? Ie, a document, or a free shipping product, etc... And do you have your cart set to not show the cart after adding a product to it.

It may not be related, but then again, it may be. Wondering if there is an impact by Stock By Attributes. Is the product(s) on which this happen controlled by SBA? Does this happen only on one browser type?

Could you possibly share a web address (and can present as www(.dot)mywebsite(dot)com or with spaces, etc...)?

[k1ra]

The product is a standard product [not document/etc]
The cart is set to not show after adding a product to it
The product is controlled by SBA

I used Firefox and Chrome

The website is under development, but a specific link to the product would be rosecityvintage(.dot)com/index.php?main_page=product_info&cPath=1_5&products_id=749