ADDITIONAL SYSTEM INFORMATION :
win10 / centos7.9

A DESCRIPTION OF THE PROBLEM :
use "list.stream().distinct().map()" ，
when I change the element value in "map()"，the "distinct()" lapsed.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Look at the Test code comment "TODO here !!" ----> ssc.setChangeFlag(1);
If I comment out the code, return 5 element.
else if I use the code, return size 4 element.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I should get 4 element of the new list theoretically.
ACTUAL -
But it return 5.

---------- BEGIN SOURCE ----------
public class Test55 {
    public static void main(String[] args) {
        List<SnStateChanged> snStateChangedList = new ArrayList<>();
        SnStateChanged ssc1 = SnStateChanged.builder().sn("1a").snChannel("1c").snVersion("1v").snYear("1y").count(1).build();
        SnStateChanged ssc2 = SnStateChanged.builder().sn("2a").snChannel("2c").snVersion("2v").snYear("2y").count(2).build();
        SnStateChanged ssc3 = SnStateChanged.builder().sn("3a").snChannel("3c").snVersion("3v").snYear("3y").count(3).build();
        SnStateChanged ssc4 = SnStateChanged.builder().sn("1a").snChannel("1c").snVersion("1v").snYear("1y").count(1).build();
        SnStateChanged ssc5 = SnStateChanged.builder().sn("1a").snChannel("1c").snVersion("1vv").snYear("1yy").count(1).build();
        snStateChangedList.add(ssc1);
        snStateChangedList.add(ssc2);
        snStateChangedList.add(ssc3);
        snStateChangedList.add(ssc4);
        snStateChangedList.add(ssc5);

        /** distinct + map */
        List<SnStateChanged> list = snStateChangedList.stream().distinct().map(ssc -> {
            // TODO here !!
            ssc.setChangeFlag(1);
            System.out.println(ssc);
            return ssc;
        }).collect(Collectors.toList());

        System.out.println(">>>>end>>>>");
    }
}

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class SnStateChanged {
    
    private Long id;

    private String sn;

    private Integer state;

    private Timestamp changeTime;

    private Integer count;

    private Integer activated;

    private Integer unbinding;

    private String snChannel;

    private String snVersion;

    private String snYear;

    private int changeFlag;

}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
split to double stream list, use ".collect(Collectors.toList())".
distinct list & map list.

FREQUENCY : always