Web Forms: Validation of mandatory xs:boolean types is not working correctly

Steps to reproduce:
1. create an XML schema that includes a mandatory (minOccurs="1" maxOccurs="1") element of type xs:boolean
2. upload the schema as a new Web Form
3. create content using the Web Form
4. don't touch the checkbox field created for the xs:boolean element
5. click ok

Expected result:

• content is saved correctly, with the xs:boolean element having a value of "false"

Actual result:

• an error message is displayed, indicating that the boolean field is mandatory but doesn't have a value

This is incorrect as it does have a value by default - an unchecked checkbox has a value of "false".