HttpServletResponseImpl.getWriter() cannot be called: getOutputStream() already called

When I invoke a RESTful web service for a not existing URI (resulting in a 404 error) I'm getting the stacktrace below. This is working fine with EAP 6.1.Beta.

In web.xml I have this declaration for a 404 error and a JSF-based error page:
<error-page>
<error-code>404</error-code>
<location>/error/pageNotFound.jsf</location>
</error-page>

Stacktrace:
12:36:03,921 SEVERE [javax.enterprise.resource.webcontainer.jsf.application] Error Rendering View[/error/pageNotFound.xhtml]: java.lang.IllegalStateException: UT010006: Cannot call getWriter(), getOutputStream() already called
at io.undertow.servlet.spec.HttpServletResponseImpl.getWriter(HttpServletResponseImpl.java:284) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at com.sun.faces.context.ExternalContextImpl.getResponseOutputWriter(ExternalContextImpl.java:834) [jsf-impl-2.2.0-m13-jbossorg-1.jar:]
at javax.faces.context.ExternalContextWrapper.getResponseOutputWriter(ExternalContextWrapper.java:785) [jboss-jsf-api_2.2_spec-2.2.0-m13.jar:2.2.0-m13]
at com.sun.faces.application.view.FaceletViewHandlingStrategy.createResponseWriter(FaceletViewHandlingStrategy.java:1166) [jsf-impl-2.2.0-m13-jbossorg-1.jar:]
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:390) [jsf-impl-2.2.0-m13-jbossorg-1.jar:]
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131) [jsf-impl-2.2.0-m13-jbossorg-1.jar:]
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337) [jboss-jsf-api_2.2_spec-2.2.0-m13.jar:2.2.0-m13]
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:337) [jboss-jsf-api_2.2_spec-2.2.0-m13.jar:2.2.0-m13]
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120) [jsf-impl-2.2.0-m13-jbossorg-1.jar:]
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) [jsf-impl-2.2.0-m13-jbossorg-1.jar:]
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219) [jsf-impl-2.2.0-m13-jbossorg-1.jar:]
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:647) [jboss-jsf-api_2.2_spec-2.2.0-m13.jar:2.2.0-m13]
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:87) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:82) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:54) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.server.HttpHandlers.executeHandler(HttpHandlers.java:46) [undertow-core-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:116) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:79)
at io.undertow.server.HttpHandlers.executeHandler(HttpHandlers.java:46) [undertow-core-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:26) [undertow-core-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.server.HttpHandlers.executeHandler(HttpHandlers.java:46) [undertow-core-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:26) [undertow-core-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:108) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchToPath(ServletInitialHandler.java:93) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.servlet.spec.RequestDispatcherImpl.error(RequestDispatcherImpl.java:367) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.servlet.spec.RequestDispatcherImpl.error(RequestDispatcherImpl.java:286) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:124) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:106) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.servlet.handlers.ServletInitialHandler.handleRequest(ServletInitialHandler.java:83) [undertow-servlet-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.server.HttpHandlers.executeRootHandler(HttpHandlers.java:52) [undertow-core-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:544) [undertow-core-1.0.0.Alpha15.jar:1.0.0.Alpha15]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [rt.jar:1.7.0_21]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [rt.jar:1.7.0_21]
at java.lang.Thread.run(Thread.java:722) [rt.jar:1.7.0_21]