We are aware of that bug, but it's got a pretty low priority compared to things on our to-do list for the main, paid E-junkie service. Fat.Free.Cart is free partially because it's an unsupported service, and that includes the matter of timely bugfixes. It's really just intended as a teaser freebie for people who want to try out the barest bones of our service with a product or two before they commit to selling more products and realize the value of what a real E-junkie cart account can do for them, but if a few people selling only one or a few products decide FFC is adequate for their needs, we're fine with that, too.
Honestly, if you're offering more than a few products, you would probably want to use the paid E-junkie cart anyway, for all the added functionality and centralized management features that gives you. IMHO it's a false economy to rely on the free cart rather than pay the $5/mo for a basic 10-product E-junkie cart, for all the labor and hassle it saves you; I certainly wouldn't want to sell more than a few products in FFC, myself and can see how the time I'd save could be better spent driving sales to my site, which would more than make up for the nominal subscription cost of E-junkie.