ToStringBuilder Works Inconsistently With HashMap

In the following code, why do the two lines containing `System.out.println(person);` yield different outputs? The second line indirectly calls the method `Job.toString` yielding the string `"Manager"`, but the first line mysteriously does not yielding `Job@28f67ac7`. The line in between `person.put("a", "b");` doesn't seem to me like it should make any difference.

Code:

{{import java.util.*;
import org.apache.commons.lang3.builder.*;

class Job extends HashMap<String, String> {
@Override public String toString()

{ return "Manager"; }

}

class Person extends HashMap<String, String> {
Job job;

Person()

{ this.job = new Job(); }

@Override public String toString()

{ return ToStringBuilder.reflectionToString(this); }

}

class Test {
public static void main(String[] args)

{ Person person = new Person(); System.out.println(person); person.put("a", "b"); System.out.println(person); }

}}}

Console:

{{Person@2b80d80f[job=Job@28f67ac7,threshold=0,loadFactor=0.75]
Person@2b80d80f[job=Manager,threshold=12,loadFactor=0.75]}}