I've spent the last few days wrestling with an evil bug. I had a content type, called Card, which I could create fine when logged in as any authenticated user of any role. All cool. I should also be able to create this content as anonymous.

Indeed, going to Create Card (node/add/card) was fine. I got the form, filled it in, but then nothing. Page Not Found where the created node was expected. The node simply wasn't created! But there were no warnings or errors. Big fat nada.