Java file.encoding on reading UTF-8 file and handling UTF-8 string

I am trying to read UTF-8 encoded XML file and pass UTF-8 string to native code (C++ dll)

My problem is best explained with a Sample program

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

public class UniCodeTest {

    private static void testByteConversion(String input) throws UnsupportedEncodingException  {    

        byte[] utf_8 = input.getBytes("UTF-8");  // convert unicode string to UTF-8
        String test = new String(utf_8);         // Build String with UTF-8 equvalent chars 
        byte[] utf_8_converted = test.getBytes();// Get the bytes: in effect this will be called in JNI wrapper on C++ side to read it in char*

        // simple workaround to print hex values
        String utfString = "";
        for (int i = 0; i < utf_8.length; i++) {
            utfString += " " + Integer.toHexString(utf_8[i]);
        }          

        String convertedUtfString = "";
        for (int i = 0; i < utf_8_converted.length; i++) {
            convertedUtfString += " " + Integer.toHexString(utf_8_converted[i]);
        }
        if (utfString.equals(convertedUtfString))   {
            System.out.println("Success" ); 
        }
        else {
            System.out.println("Failure" ); 
        }
    }

    public static void main(String[] args) {
        try {
              File inFile = new File("c:/test.txt");
              BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream(inFile), "UTF8"));
              String str;
              while ((str = in.readLine()) != null) {
                  testByteConversion(str);
              }
              in.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

and the test file has stored in UTF-8 format (Tamil Locale)

#just test
 நனமை
 நன்மை

I did the following experiments:

1. set file.encoding property to 'UTF-8' I get success for both inputs

2. when I set file.encoding to 'CP-1252' First input, i get 'Success' and for the second input I am getting 'Failure'

Here is what I got for the failure case

utf_8           :  e0 ae a8 e0 ae a9 e0 af 8d e0 ae ae e0 af 88
utf_8_converted :  e0 ae a8 e0 ae a9 e0 af 3f e0 ae ae e0 af 88

I do not understand why 8d is converted into 3f when file.encoding set to CP-1252. Can any one please explain me

I miss the link between file.encoding and string manipulation

Thanks in advance :)