I have encountered an interesting "problem" whereby I have attributes set for some of our products and on each list I have a "Select your colour" set as a default non selectable. If the user inadvertently chooses this and clicks update, the correct response is displayed saying "Please correct the following: On the Option for: Colour You picked an Invalid Selection: Select required Colour"
If the users then corrects the mistake by choosing a colour and clicking update the cart is emptied and takes the user back to the products page.

I am not too concerned about this personally, but it may to someone else.

Zen 1.3.8a