Non-selected variants appearing in cart

Hi,
The products in our store all have optional variants i.e. you can order a product with optional 1 year, 2 year or 3 year subscription or no subscription at all.
I have set this up by declaring a characteristic called Annual Subscription with variants of 1 year, 2 years and 3 years, each of which has a price. The fourth variant is called None and is unpriced. None is the default value for the Annual Subscription.

The problem I have is that when I 'add to cart' from the main product description, two products appear in the cart, even when I have not selected any subscription i.e. the default value of None is active.

This is confusing because the customer will think they have two products in the cart when in fact they really have only one. The second product is 'None' and is not chargeable.

Is there any way I can avoid this and not select an optional variant at all from the product page?

I attach a test dataset which hopefully will illustrate the problem.

Regards
PhilP