If you’re using HTML Validate (you should; it’s ace), update to 7.15.2. It no longer flags multiple buttons with the same name used in forms as a validation error (this is a valid pattern that lets you interpret a form differently on the server based on which button it was submitted with).
PS. Kitten uses HTML Validate to show you validation issues with your pages as you develop.
@aral How does this compare to running the Nu HTML Checker offline? Are there errors this will flag which vNu won’t?