When multiple <authentication-manager> elements are defined the second one overrides the first one. The only indication is WARNING logged.
WARN org.springframework.beans.factory.parsing.FailFastProblemReporter - Configuration problem: Overriding globally registered AuthenticationManager
It would be better to either fail or better yet support multiple <authentication-manager> elements. The work around is to create only one AuthenticationManager with the namespace and to create other AuthenticationManager's with standard Spring bean configuration.