FormBuilder: Server-side validation doesn't work
I've observed two different patterns on the master branch, but never the correct behavior.
Scenario 1
Basic FormBuilder form with a required date field. Date field doesn't properly client-side validate (see #4173 (closed)) so it's submitted. Server-side validation returns a 500 error. An unhelpful alert appears.
Scenario 2
Upon submitting, server-side validation is completely ignored and the form is submitted. I believe this happens when you have a non-required File field on the page.
Here is FormBuilder markup for both scenarios: scenario1-markup scenario2-markup