FULL PRODUCT VERSION :
java version "1.7.0_45"
Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
$ uname -a
Linux ayanichkin-desktop 3.11.0-14-generic #21-Ubuntu SMP Tue Nov 12 17:04:55 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

A DESCRIPTION OF THE PROBLEM :
I need custom 1-byte charset, that actually stored in database. But when I attempt encode some text with it, I received IllegalArgumentException (some inputs processed correctly always, some only sometimes).

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Use attached source code of 1-byte table charset. Output copied from http://www.compileonline.com/compile_java_online.php, but on my machine this also fails.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Encoded byte array with my charset.
ACTUAL -
# Compiling the source code....
$javac Table1ByteCharset.java 2>&1

# Executing the program....
$java -Xmx128M -Xms16M Table1ByteCharset
Exception in thread "main" java.lang.IllegalArgumentException
at java.nio.Buffer.position(Buffer.java:236)
at java.nio.charset.CharsetEncoder.encode(CharsetEncoder.java:600)
at java.lang.StringCoding.encode(StringCoding.java:370)
at java.lang.String.getBytes(String.java:939)
at Table1ByteCharset.main(Table1ByteCharset.java:56)

REPRODUCIBILITY :
This bug can be reproduced often.

---------- BEGIN SOURCE ----------
import java.util.Arrays;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CoderResult;

public class Table1ByteCharset extends Charset {
    // Encode each char with its position in table, [0; 255].
    final char[] table = new char[255];
    class Encoder extends CharsetEncoder {
        Encoder() {
            super(Table1ByteCharset.this, 1.0f, 1.0f, new byte[]{(byte)'?'});
        }
        @Override
        protected CoderResult encodeLoop(CharBuffer in, ByteBuffer out) {
            while (in.remaining() > 0) {
                if (out.remaining() == 0) {
                    return CoderResult.OVERFLOW;
                }
                final int b = indexOf(in.get());
                if (b < 0) {
                    return CoderResult.unmappableForLength(1);
                }
                out.put((byte)b);
            }
            return CoderResult.UNDERFLOW;
        }
    }
    class Decoder extends CharsetDecoder {
        Decoder() {
            super(Table1ByteCharset.this, 1.0f, 1.0f);
        }
        @Override
        protected CoderResult decodeLoop(ByteBuffer in, CharBuffer out) {
            while (in.remaining() > 0) {
                if (out.remaining() == 0) {
                    return CoderResult.OVERFLOW;
                }
                out.put(table[ index(in.get()) ]);
            }
            return CoderResult.UNDERFLOW;
        }
        private int index(byte b) {return b < 0 ? 256 + (int)b : (int)b;}
    }
    Table1ByteCharset() {super("Table1ByteCharset", null);}
    @Override
    public boolean contains(Charset cs) {return this == cs;}
    
    @Override
    public Encoder newEncoder() {return new Encoder();}
    @Override
    public Decoder newDecoder() {return new Decoder();}

    public static void main(String[] args) {
        System.out.println(Arrays.toString("Hello World".getBytes(new Table1ByteCharset())));
    }
    int indexOf(char ch) {
        for (int i = 0; i < table.length; ++i)
            if (table[i]==ch) return i;
        return -1;
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
In my case I just not use Charset subclass.