Description:
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I am unable to properly encode certain strings from ISO-8859-1 to UTF-8. I have tried using utf8_encode, mb_convert_encoding and iconv with no success. The code I am attempting this on is as follows:

Reproduce code:
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<?php
$main_test_string = "r?f?rendum sur la Constitution europ?enne";
$string_test = mb_detect_encoding($main_test_string, 'UTF-8, ISO-8859-1');
echo "Encoding used: $string_test<br>"; // Properly displays ISO-8859-1

// First try converting with iconv
$iconv_test = iconv("ISO-8859-1", "UTF-8", $main_test_string);
echo "Iconv test: $iconv_test<br>"; // Displays nothing. No data whatsoever

// Now try converting with mb_convert_encoding
$mb_test = mb_convert_encoding($main_test_string, "UTF-8", "ISO-8859-1");
$string_test2 = mb_detect_encoding($mb_test, 'UTF-8, ISO-8859-1'); 
echo "Encoding used: $string_test2<br>"; // Indicates string is now UTF-8 encoded (which is wrong)
echo "MB Test convert value: $mb_test<br>"; // Displays: référendum sur la Constitution européenne; doesn't look like UTF-8 to me

// Finally try utf8_encode
$utf8_encode_test = utf8_encode($main_test_string);
$string_test3 = mb_detect_encoding($textfieldabstract, 'UTF-8, ISO-8859-1');
echo "Encoding used: $string_test3<br>"; // Indicates string is now UTF-8 encoded (which is wrong)
echo "Abstract post conversion: $utf8_encode_test<br>"; // Same as before, displays: référendum sur la Constitution européenne 
?>

Expected result:
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I should be seeing UTF-8 (Unicode) translated text of the style:
'&#917;&#955;&#955;&#951;&#957;&#953;'

Note that the above does work for non-latin based character sets like chinese, japanese, russian, greek, etc.

Actual result:
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What I am seeing is the following string:

référendum sur la Constitution européenne

Definately not UTF-8. Could be Klingon. :-)

I will admit I am not a Unicode master but this is certainly quite puzzling. According to the documentation, iconv is supposed to work in this case but it is not displaying any data. I am running PHP 5.0.4 with iconv enabled. (I see it in my phpinfo output)

Please advise.