pq on "[Plugin: Contact Form 7] Form submits with empty required text fields"

Hello,
I'm using WPCF7 for simple email signups. The form only has 4 fields: first, last, email, and and zip code; and all are required. In spite of the asterisks on all of the text fields, the form can be submitted with only an email address. If submitted entirely empty, only the email address will reliably return an error - and even then, the error is the invalid address one, not the required field.

Code is very standard:

[text* firstname placeholder "First Name"]
[text* lastname placeholder "Last Name"]
[email* email placeholder "Email Address"]
[text* zip placeholder "Zip Code"]

https://wordpress.org/plugins/contact-form-7/