Autowiring by constructor in Spring creating more objects

I am creating a demo to understand that how can i inject a prototype bean into a singleton bean by using constructor autowiring. Here is my code My First bean is

public class IndependentBean {
    private String independentName;
    public IndependentBean()
    {
        System.out.println("Independent called");
    }

    public String getIndependentName() {
        return independentName;
    }

    public void setIndependentName(String independentName) {
        this.independentName = independentName;
    }
}

Now I am creating an independent bean

package com.sample.beans;

public abstract class DependentBean {
    private IndependentBean d1;
    private IndependentBean d2;
    public DependentBean()
    {
        System.out.println("Default Constructor for dependent");
    }
    public IndependentBean getD1() {
        return d1;
    }

    public void setD1(IndependentBean d1) {
        System.out.println("Setting d1");
        this.d1 = d1;
    }

    public IndependentBean getD2() {
        return d2;
    }

    public void setD2(IndependentBean d2) {
        System.out.println("Setting d2");
        this.d2 = d2;
    }

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public DependentBean(IndependentBean d1) {
        System.out.println("With 1");
        this.d1 = d1;
    }

    public DependentBean(IndependentBean d1, IndependentBean d2) {
        this.d1 = d1;
        this.d2 = d2;
        System.out.println("With 2");
    }
} 

Here is my context.xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://ift.tt/GArMu6"
    xmlns:xsi="http://ift.tt/ra1lAU" xmlns:context="http://ift.tt/GArMu7"
    xmlns:aop="http://ift.tt/OpNdV1"
    xsi:schemaLocation="http://ift.tt/GArMu6 http://ift.tt/1jdM0fG
        http://ift.tt/GArMu7 http://ift.tt/1tY3uA9
        http://ift.tt/OpNdV1 http://ift.tt/1oTOpwm">
    <bean class="com.sample.beans.IndependentBean" id="firstIn" scope="prototype">
        <property name="independentName" value="firstIndependent" />
    </bean>

    <bean class="com.sample.beans.DependentBean" id="autowireByConstructor"
        autowire="constructor">
        </bean>
</beans>

Here is my main class

package com.sample.beans;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainClass {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext(
                "classpath:context.xml");
        ctx.getBean("autowireByConstructor");
        ctx.close();
    }

}

According toSpring spec I know that when i am working with autowiring with constructor the constructor with satisfying most dependencies will be called. However in this case the constructor of independent bean should be call 2 times.but in my case the constructor is called 4 times. I am not getting this clearly.Please help me to understand this ?

Here is the output of the code:

Independent called

Independent called

Independent called

Independent called

With 2

Please help me to understand this behaviour.