Grunion ignores my extra fields

The topic title says it all. I set up a form that looks like this:

[contact-form subject="Website Contact" to="xxxxxxxx@gmail.com"]
[contact-field label="Name" type="name" required="true" /]
[contact-field label="Email Address" type="email" required="true" /]
[contact-field label="Phone Number" type="text" /]
[contact-field label="School/Company/Organization" type="text" /]
[contact-field label="Message" type="textarea" /]
[contact-field label="I would use your product in:" type="radio" options="School District,Afterschool Program,Library Program,Museum or other Cultural Institution,Other" /]
[/contact-form]

All the form elements appear as expected on the page.

But when I send the message, I only get the Name, Email, Website, and Message fields (the default set) in the email. A dead giveaway is that “Website” is not even included in the shortcode above but it shows up in the email that I receive.

Any ideas?