Products with non-required attributes can be added to cart without ANY attributes, unlike when using regular Ubercart

Ajax Cart only stops you from adding products to your cart without selecting attributes if there are attributes set as REQUIRED on the item.

The standard Ubercart behavior is to redirect you to the product page if there are ANY attributes associated with the item. This allows you to set attributes with default settings, yet still allow the user to change them to select other options (setting an attribute as "required" ignores the default option, and lists "please select" instead).

Currently when using Ajax Cart, if you have items with attributes and none of them are marked as "required," there is no way to keep the customer from ordering the product without any attributes at all. The only workaround is to set one of those attributes to "required," so that Ajax cart redirects to to the product page and forces a selection. Doing this prevents you from having one of the options set as default for that attribute.