Java Deserialisation anomaly

Question

I have an Issue deserialising a Java Instance with 3 fields.
2 of the fields are being deserialised as I would expect.

The 3rd is being initialised as defined in the Class.
I would expect it to be deserialised too.

I am using openJDK 17.

Below is some example code.

1. Run the Programme as is
2. WAIT a few seconds
3. comment in & out as indicated (3 TODO's) & run again

First time through I get this:

11:09:02 SerialTest then.: 11:09:02.870987 msThen.: 1680685742677 msNow.: 1680685742988
11:09:04 SerialTest then.: 11:09:02.870987 msThen.: 1680685742677 msNow.: 1680685744990
11:09:06 SerialTest then.: 11:09:02.870987 msThen.: 1680685742677 msNow.: 1680685746992
11:09:08 SerialTest then.: 11:09:02.870987 msThen.: 1680685742677 msNow.: 1680685748993
11:09:10 SerialTest then.: 11:09:02.870987 msThen.: 1680685742677 msNow.: 1680685750994

Second time, this:

11:09:40 Why this?! then.: 11:09:02.870987 msThen.: 1680685742677 msNow.: 1680685780744
11:09:42 Why this?! then.: 11:09:02.870987 msThen.: 1680685742677 msNow.: 1680685782747
11:09:44 Why this?! then.: 11:09:02.870987 msThen.: 1680685742677 msNow.: 1680685784749
11:09:46 Why this?! then.: 11:09:02.870987 msThen.: 1680685742677 msNow.: 1680685786751
11:09:48 Why this?! then.: 11:09:02.870987 msThen.: 1680685742677 msNow.: 1680685788751

The "then" Millis & LocalTime are being deserialised as I had expected & remain constant.
Can anyone help me to understand why className is not being deserialised?

import java.io.*;
import java.nio.file.*;
import java.time.*;
import java.time.temporal.*;

public final class SerialTest implements Serializable {

    private static final long    serialVersionUID = -5422947008060509280L;
    private static final Path    PATH             = Path.of("SerialTest.ser");

    public         final long    millisThen       = System.currentTimeMillis();
    public         final String  dateTimeThen     = LocalTime.now().toString();

    public         final String  className        =  SerialTest.class.getName(); // TODO Comment out
//  public         final String  className        = "Why this?!";                // TODO Comment in

    public static void main(final String[] args) throws Exception {

        Files.write(PATH, new SerialTest().serialize()); // TODO Comment out

        deserialize();    sleep(Duration.ofSeconds(2));
        deserialize();    sleep(Duration.ofSeconds(2));
        deserialize();    sleep(Duration.ofSeconds(2));
        deserialize();    sleep(Duration.ofSeconds(2));
        deserialize();    sleep(Duration.ofSeconds(2));
    }

    private static void sleep(final Duration duration) {
        try {Thread.sleep(duration.toMillis());} catch (final Exception e) {}
    }

    private static void deserialize() throws Exception {

        final InputStream ist = new  ByteArrayInputStream(Files.readAllBytes(PATH));

        final SerialTest  ser = (SerialTest) new ObjectInputStream(ist).readObject();

        System.out.print  (""           + LocalTime.now().truncatedTo(ChronoUnit.SECONDS));
        System.out.print  (" "          + ser.className);
        System.out.print  (" then.: "   + ser.dateTimeThen);
        System.out.print  (" msThen.: " + ser.millisThen);
        System.out.println(" msNow.: "  + System.currentTimeMillis());
    }

    public byte[] serialize() throws IOException {

        final ByteArrayOutputStream baos = new ByteArrayOutputStream();
        final    ObjectOutputStream oos  = new    ObjectOutputStream(baos);

        try {
            oos.writeObject(this);
        }
        finally {
            oos.close();
        }
        return baos.toByteArray();
    }
}