Why do HashSets not have a stable serialization?

Take a HashSet in Java. Put a string in it. Serialize it. You end up with some bytes - bytesA.

Take bytesA, deserialize it back as an Object - fromBytes.

Now reserialize fromBytes and you've got yourself another array of bytes - bytesB.

Strangely enough, these two byte arrays are not equal. One byte is different! Why? Interestingly, this does not affect TreeSet or HashMap. It does however affect LinkedHashSet.

Set<String> stringSet = new HashSet<>();
stringSet.add("aaaaaaaaaa");

//Serialize it
byte[] bytesA;
try (ByteArrayOutputStream bos = new ByteArrayOutputStream()) {
  ObjectOutputStream out = new ObjectOutputStream(bos);
  out.writeObject(stringSet);
  out.flush();
  bytesA = bos.toByteArray();
}

// Deserialize it
Object fromBytes;
try (ByteArrayInputStream is = new ByteArrayInputStream(bytesA)) {
  try(ObjectInputStream ois = new ObjectInputStream(is)) {
    fromBytes = ois.readObject();
  }
}

//Serialize it.
byte[] bytesB;
try (ByteArrayOutputStream bos = new ByteArrayOutputStream()) {
  ObjectOutputStream out = new ObjectOutputStream(bos);
  out.writeObject(fromBytes);
  out.flush();
  bytesB = bos.toByteArray();
}

assert Arrays.equals(bytesA, bytesB); 

//array contents differ at index [43], expected: <16> but was: <2>

In case these help: xxd hex dump of bytesA

00000000: aced 0005 7372 0011 6a61 7661 2e75 7469  ....sr..java.uti
00000010: 6c2e 4861 7368 5365 74ba 4485 9596 b8b7  l.HashSet.D.....
00000020: 3403 0000 7870 770c 0000 0010 3f40 0000  4...xpw.....?@..
00000030: 0000 0001 7400 0a61 6161 6161 6161 6161  ....t..aaaaaaaaa
00000040: 6178                                     ax

xxd hex dump of bytesB

00000000: aced 0005 7372 0011 6a61 7661 2e75 7469  ....sr..java.uti
00000010: 6c2e 4861 7368 5365 74ba 4485 9596 b8b7  l.HashSet.D.....
00000020: 3403 0000 7870 770c 0000 0002 3f40 0000  4...xpw.....?@..
00000030: 0000 0001 7400 0a61 6161 6161 6161 6161  ....t..aaaaaaaaa
00000040: 6178                                     ax

3rd line 6th column is the difference.

I'm on Java 11.0.3.

(RESOLVED)

As per Alex R's response - what happens is that HashSet's writeObject stores the capacity, loadFactor, and size of the backing HashMap, but its readObject recalculates the capacity as:

capacity = (int)Math.min((float)size * Math.min(1.0F / loadFactor, 4.0F), 1.07374182E9F);

Other than a sanity check, it actually ignores the capacity value that was originally stored!