Can't find bundle for base name filename.properties, locale en_US

Issue

• Can't find bundle for base name phonebook, locale en_US
• After migrating from EAP 5 to EAP 6, ResourceBundle.getBundle().getString() stopped working with this exception:

ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/TestApplicationWebTest].[dispatcher]] (localhost/127.0.0.1:8080-1) JBWEB000235: Allocate exception for servlet dispatcher: java.util.MissingResourceException: Can't find bundle for base name filename.properties, locale en_US
    at java.util.ResourceBundle.throwMissingResourceException(ResourceBundle.java:1499) [rt.jar:1.7.0_67]
    at java.util.ResourceBundle.getBundleImpl(ResourceBundle.java:1322) [rt.jar:1.7.0_67]
    at java.util.ResourceBundle.getBundle(ResourceBundle.java:721) [rt.jar:1.7.0_67]