Smartcards - single and return ticktes

I have an annual season on a smartcard. The option exists on your ticket machines to buy day single and return tickets between smart-enabled stations. However, although they can be bought with the Network Railcard and other railcard discounts, the Gold Card option is greyed out and not available. This seems complete nonsense given that the vast majority of smartcard holders are going to be annual Gold Card holders! Why is this?