java serialization random access, a very strange thing！

I plan to use ByteArrayOutputStream to write Objects to byte array, then write the byte array to a file. I keep the position of each Object. Then I read from the file, using FileInputStream.getChannel().position() to relocate the position, and call ObjectInputStream.readObject().

Here is my test code:

public static void main(String[] args) {
    try {
        HashBucketTest bucket1 = new HashBucketTest();
        bucket1.putAddress("0", 30);

        HashBucketTest bucket2 = new HashBucketTest();   // bucket2 key is the same as bucket3
        bucket2.putAddress("22313", 40);

        HashBucketTest bucket3 = new HashBucketTest();
        bucket3.putAddress("22313", 50);

        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oops = new ObjectOutputStream(baos);

        FileOutputStream fout = new FileOutputStream("objects.txt");
        BufferedOutputStream bs = new BufferedOutputStream(fout);

        int position1 = baos.size();                                // the first object position
        bs.write(baos.toByteArray());                               // write head
        baos.reset();

        oops.writeObject(bucket1);                  // write the first object to byte array
        int position2 = position1 + baos.size();    // the second object position
        bs.write(baos.toByteArray());               // write first object to file
        baos.reset();

        oops.writeObject(bucket2);                  // write the second object to byte array
        int position3 = position2 + baos.size();    // the third object position
        bs.write(baos.toByteArray());               // write the second object to file
        baos.reset();

        oops.writeObject(bucket3);                  // write the third object to byte array
        int position4 = position3 + baos.size();    // the fourth object position
        bs.write(baos.toByteArray());               // write the third object to file
        baos.reset();

        bs.flush();
        bs.close();
        fout.flush();
        fout.close();

        // read according to the position x

        HashBucketTest readCase1 = null;
        HashBucketTest readCase2 = null;
        HashBucketTest readCase3 = null;

        FileInputStream fis = new FileInputStream("objects.txt");
        ObjectInputStream ois = new ObjectInputStream(
                fis);

        // success case
        readCase1 = (HashBucketTest) ois.readObject();  // read the first object, success
        fis.getChannel().position(position2);
        readCase2 = (HashBucketTest) ois.readObject();  // read the second object, success
        fis.getChannel().position(position3);
        readCase3 = (HashBucketTest) ois.readObject();  // read the third object, success

        // failed case!!!!
        //readCase1 = (HashBucketTest) ois.readObject();    // read the first object, success
        //fis.getChannel().position(position3);
        //readCase3 = (HashBucketTest) ois.readObject();    // read the third object, failed!!
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

public static class HashBucketTest implements Serializable {

    private static final long serialVersionUID = 3610182543890121796L;

    Map<String, Integer> values = null; // need to write to disk

    public HashBucketTest() {

        values = new TreeMap<String, Integer>();
    }

    public void putAddress(String key, int number) {

        values.put(key, number);
    }

}

My problem is, when the key of "bucket2" is the same as "bucket3"( "22313" in this case). I can't read bucket3 skippting bucket2

java.io.StreamCorruptedException: invalid handle value: 007E000C
at java.io.ObjectInputStream.readHandle(ObjectInputStream.java:1456)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1331)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
at java.util.TreeMap.buildFromSorted(TreeMap.java:2563)
at java.util.TreeMap.buildFromSorted(TreeMap.java:2504)
at java.util.TreeMap.readObject(TreeMap.java:2450)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1017)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1896)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1801)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1993)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1918)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1801)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
at com.alibaba.middleware.benchmark.Test.main(Test.java:146)

But if the key is different, I can do this successfully. It seems bucket3's key refer to the bucket2's? that's very strange. And in any case, sequential reading is ok, but I dont want sequential reading.