Can't change forum display name?

This is a question about using this forum rather than the app, but I couldn't find a forum section for that.  I've just joined after ordering my first Sisyphus table, and I'm trying to complete my account.  Under Account Settings, I have fields for first and last name, email, and then fields for changing my password.  When I try to save changes there, I get an error that "Display name is a required field" -- except that field isn't shown on the form.