Berkeley DB Family

I'll find this result that I cannot understand:
when I put a record with the same key and the same data (a custom comparator return 0) in a database, if there is only one record for a given key the put method correctly overrides the data, if there is more then one record with the same key the put doesn't override the data.

This is an example:

public class DBTest {


private static Environment env;
private static Database store;

/* The comparator */
static class MyComparator implements Comparator,Serializable {

public int compare(Object o1, Object o2) {
byte[] b1=(byte[]) o1;
byte[] b2=(byte[]) o2;

return b1[0]-b2[0];
}

}


/* Used for printing the result */
static String byteview(byte[] b) {
StringBuffer sb=new StringBuffer("[");
for(int i=0;i<b.length;i++) {
if(i>0) sb.append(',');
sb.append(Byte.toString(b[ i]));
}
sb.append(']');
return sb.toString();
}




public static void main(String[] args) {

EnvironmentConfig envConfig = new EnvironmentConfig();
envConfig.setTransactional(true);
envConfig.setAllowCreate(true);
envConfig.setCacheSize(1000000);

try {
env = new Environment(new File("E:\\Knowledgebase\\DEACache\\"), envConfig);
DatabaseConfig dataConfig = new DatabaseConfig();
dataConfig.setAllowCreate(true);
dataConfig.setSortedDuplicates(true);
dataConfig.setOverrideDuplicateComparator(true);
dataConfig.setDuplicateComparator(new MyComparator());
store = env.openDatabase(null, "_data_", dataConfig);

DatabaseEntry k=new DatabaseEntry();
DatabaseEntry d=new DatabaseEntry();

k.setData(new byte[]{0,1,2});
d.setData(new byte[]{0,0,1,2,3,4});
store.put(null, k, d);

k.setData(new byte[]{0,1,2});
d.setData(new byte[]{0,0,1,4,2,3});
store.put(null, k, d);

k.setData(new byte[]{0,1,2});
d.setData(new byte[]{1,0,10,20});
store.put(null, k, d);

k.setData(new byte[]{0,1,2});
d.setData(new byte[]{1,0,25,35});
store.put(null, k, d);

// print the content of the database (2 record)
Cursor c=store.openCursor(null, null);
c.getFirst(k, d, LockMode.DEFAULT);
System.out.println("key:"+byteview(k.getData())+" data:"+byteview(d.getData()));
while(c.getNext(k, d, LockMode.DEFAULT)==OperationStatus.SUCCESS) {
System.out.println("key:"+byteview(k.getData())+" data:"+byteview(d.getData()));
}
c.close();


k.setData(new byte[]{0,1,2});
d.setData(new byte[]{0,0,4,3,2,1});
store.put(null, k, d);

k.setData(new byte[]{0,1,2});
d.setData(new byte[]{1,0,40,30,20,10});
store.put(null, k, d);

// print the content of the database (2 record)
c=store.openCursor(null, null);
c.getFirst(k, d, LockMode.DEFAULT);
System.out.println("key:"+byteview(k.getData())+" data:"+byteview(d.getData()));
while(c.getNext(k, d, LockMode.DEFAULT)==OperationStatus.SUCCESS) {
System.out.println("key:"+byteview(k.getData())+" data:"+byteview(d.getData()));
}
c.close();

}
catch (DatabaseException e) {
e.printStackTrace();
}


}

}

When I run this program I have those results:

key:[0,1,2] data:[0,0,1,4,2,3] correct, it overrides
key:[0,1,2] data:[1,0,10,20] strange, should be [1,0,25,35]
key:[0,1,2] data:[0,0,1,4,2,3] strange, should be [0,0,4,3,2,1]
key:[0,1,2] data:[1,0,10,20] strange, should be [1,0,40,30,20,10]

Do I have miss somethings?

Thank-you in advance