I think I finally beat Cafe Press's censorship algorithm. It turns out, I'd named the actual design file "ketchup.jpg". I uploaded it again, exactly the same, but under the new moniker: "lunch.jpg". Bang. Boom. Shirt's up. You can buy it. Always good to buy repressed art, right?
Lesson learned? Keep brands out of your file-naming scheme. I wonder if they do actually look at the design content in any automated way, hmm. . .