Why @ManagedBean works while @Named doesn't?

I am reading the book Core Java Server Faces 3rd Edition.
There is a sample of JSF ajax feature and I tried it with NetBeans9.1 and GlassFish V3.
However only when I use @ManagedBean, it works well. If I use @Named annotation, it seems that the @SessionScoped annotation doesn't work.
Because I saw that the default constructor of User bean was called four times when I click the Login button and the getGreeting() cannot catch the filed "name"'s value.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
       xmlns:h="http://java.sun.com/jsf/html"
       xmlns:f="http://java.sun.com/jsf/core">
    <h:head>
       <title>Welcome</title>
    </h:head>
    <h:body>
       <h:form prependId="false">
          <h3>Please enter your name and password.【#{user.name}】</h3>
          <table>
              <tr>
                 <td>Name:</td>
                 <td><h:inputText value="#{user.name}" id="name"/></td>
              </tr>
              <tr>
                 <td>Password:</td>
                 <td><h:inputSecret value="#{user.password}" id="password"/></td>
              </tr>
           </table>
          <p>
            <h:commandButton value="Login">
              <f:ajax execute="name password" render="out"/>
            </h:commandButton>
          </p>
          <h3><h:outputText id="out" value="#{user.greeting}"/></h3>
       </h:form>
    </h:body>
</html>

When I use @ManagedBean everything is ok:

When I use @Named instead, it is not ok anymore:

too many times the constructor method was called in each request.

I might be on the wrong track here but here goes

Perhaps you use the same @SessionScoped annotation on both cases? Does the example you use do the same thing?

I have understood that if you use the @Named annotation (and are using the J2EE CDI (Contexts and Dependency Injection)) you should use the annotation used with enterprise beans i.e.
@javax.enterprise.context.SessionScoped

and if you use the @ManagedBean annotation (that is a JSF thing and not a "J2EE wide annotation") you use the JSF annotation meant for JSF beans i.e.
@javax.faces.bean.SessionScoped

@ManagedBean is a JSF annotation and it wires itself into the faces-config. @Named is not. Although I believe that @Named can be used to set the management name of the bean instance, it doesn't inherently wire in to the JSF bean management subsystem.

I had the same issue and the @Named annotation started working correctly after I've included an empty beans.xml file under WEB-INF. Now I just use the @Named annotation and don't use @ManagedBean no longer.

I use NetBeans IDE, so a beans.xml was automatically included in WEB-INF directory. I guess this is not the point.
I tried to replace the import declaration of SessionScope from javax.faces.bean.SessionScoped to javax.enterprise.context.SessionScoped and it worked.

Thanks for your help.