mb_convert_encoding converting to ASCII instead of UTF-8

I've run into a problem where mb_convert_encoding seems to be converting to ASCII, even though I'm telling it to convert to UTF-8. This is with PHP version 4.3.11. I had been asking it to convert from "auto" to UTF-8, so at first I thought maybe "auto" was not the right choice. So I called "mb_detect_encoding" to see the format of what I was trying to convert; it said it was already UTF-8 (before I did the conversion). So then I thought maybe I got the "from" and "to" parameters backwards (although I was confident I was following the documentation), so I changed mb_convert_encoding to use "UTF-8" as /both/ the from and to. It still converts to ASCII. I understand that, given that it's already UTF-8, I don't need to convert it to UTF-8. But other things that I receive might /not/ be UTF-8, so I am still concerned with this. Sample code: <html><head><title>Minnie</title></head><body><p> <?php $x = $_REQUEST['Minnie']; echo $x . ' ... ' . mb_detect_encoding ( $x ) . '<br/>'; $x = mb_convert_encoding ( $x, "UTF-8", "UTF-8" ); echo $x . ' ... ' . mb_detect_encoding ( $x ) . '<br/>'; ?> </p></body></html> Output, when called with URL parameter "Minnie=Miñoso": Miñoso ... UTF-8 Mioso ... ASCII Then I changed the "from" so that I could try converting from something other than UTF-8: $x = mb_convert_encoding ( $x, "UTF-8", mb_detect_encoding ( $x ) ); And now, output when called with "Minnie=Mouse": Mouse ... ASCII Mouse ... ASCII Does anyone have any idea what's going on here? Am I doing something wrong? Thanks in advance for any help.