keystone-classic: Boolean default:true value not working in v4.0.0

Expected behavior

Add a checkbox which is checked by default. Clicking on it should uncheck the box.

Actual/Current behavior

Clicking on the checked by default box does not uncheck it.

Steps to reproduce the actual/current behavior

Add a model with a Boolean field with default value set to true:

import keystone from 'keystone';
const Types = keystone.Field.Types;
const Page = new keystone.List('Page');

Page.add({
	show  : { type: Types.Boolean, label: 'Show this page?', default: true, initial: true }
});
Page.register();

Try and uncheck the checkbox.

Environment

Software	Version
Keystone	4.0.0
Node.js	9.3.0
Browser	Chrome 67