Product Attributes Not Selected in Cart using Fast and Easy AJAX Checkout 2

I am having the same trouble elaborated in this thread:
http://www.zen-cart.com/showthread.php?208632

The problem occurs infrequently enough to pinpoint but I have checked all attributes and they are configured consistently.
All products must have an attribute selected to add to cart.

Here is an example of the error:

Products

1 x Italian Street Fair Spice Blend = $0.00

1 x Florida Sunshine Spice Blend = $0.00

2 x Vik's Garlic Fix! Spice Blend = $10.38
size 1 ounce bag

1 x Adobo Spice Blend = $5.19
size 1 ounce bag

1 x California Spice Blend = $5.19
size 1 ounce bag

1 x English Roast Rub = $5.19
size 1 ounce bag

1 x Chef's Choice Steak Rub (2-BND082917-BDL) = $5.19
size 1 ounce bag

1 x Coastal Blend Seasoning = $5.19
size 1 ounce bag

1 x Herb Sesame Spice Blend = $5.19
size 1 ounce bag

1 x Lamb & Pork Seasoning = $5.19
size 1 ounce bag

1 x Mushroom Paradise Spice Blend = $5.19
size 1 ounce bag

However, since I am using v1.5.0, the fix is included in my code base.
The difference seems to be in the Fast and Easy Checkout AJAX module, but this module doesn't override shopping_cart.php or order total module.

Just because a plugin doesn't override a module doesn't mean that it's not making changes via notifier-hooks. Since the Fast and Easy Ajax Checkout is a commercial plugin, I suggest that you contact the author (numinix) to see what's up.

I have a ticket in with the vendor, however, I'm not sure it is that module causing the problem.
It seems to be related to stored carts of returning users and I have not been able to duplicate the error.