Java ProcessBuilder/Runtime.exec fails to correctly pass string arguments to the process on Windows?

Question

It seems like java fails to correctly encode Strings when ProcessBuilder or Runtime.exec pass them along to the process they spawn, even with -Dfile.encoding set - for reasons that I don't understand. This means high codepoint characters (Chinese, Japanese etc) don't passed along to the child process.

As a simple example, compile the following two test classes, substituting in your own jre in Test1 and whatever file path you like in Test2:

import java.io.IOException;
import java.nio.charset.Charset;

public class Test1 {
    public static void main(String[] args) throws IOException {
        String s = "因";
        System.out.println(bytesToHex(s.getBytes(Charset.forName("UTF-8"))));
        Runtime.getRuntime().exec(new String[]{"C:\\Program Files\\Java\\jdk1.6.0_45\\bin\\java.exe", "-cp", ".", "Test2", s});
    }

    public static String bytesToHex(byte[] bytes) {
        char[] hexArray = "0123456789ABCDEF".toCharArray();
        char[] hexChars = new char[bytes.length * 2];
        for ( int j = 0; j < bytes.length; j++ ) {
            int v = bytes[j] & 0xFF;
            hexChars[j * 2] = hexArray[v >>> 4];
            hexChars[j * 2 + 1] = hexArray[v & 0x0F];
        }
        return new String(hexChars);
    }
}

and

import java.io.FileWriter;
import java.io.IOException;
import java.nio.charset.Charset;

public class Test2 {
    public static void main(String[] args) throws IOException {
        FileWriter w = null;
        try {
            w = new FileWriter("<some directory>\\testoutput.txt");
            w.write(Test1.bytesToHex(args[0].getBytes(Charset.forName("UTF-8"))));
        } finally {
            if (w != null) w.close();
        }
    }
}

Then run Test1:

java -Dfile.encoding=UTF-8 Test1

Observe that Test1 prints out "E59BA0", whilst Test2 writes "3F" ('?') to file.

Can anyone explain why this is, and what the correct way to accomplish what I want to accomplish is?