Component with overriden isRequired method does not evaluate plain string value

Component with overriden isRequired() method using "required" instead PropertyKeys.required string as in UIInput parent class (you can add default value here if attribute is not found or set). Works with #{true} or #{xxxController.isComponentRequired} but not with plain string like "true".

See ThirdComponent in attached example. You can execute the sample with mvn jetty:run -Pmyfaces40 command and hit http://localhost:8080/primefaces-test to run the page.