Not selecting a required radio button throws no error

Steps to reproduce

1. Create a custom field of type Radio Button and add some options to it. Do not set a default option.
2. Add this field as a required field on a form
3. Fill out the form, but do not select any options for this field.
4. Hit Submit

Expected behaviour

Form fails to validate and throws an error message (as it does with other custom field types)

Actual behaviour

Form fails to validate (correctly) but throws no error message. The Service Desk request will not be created.