I see the problem now

It is a bug in CGI

        # See RFC 1867, 2183, 2045
        # NB: File content will be loaded into memory should
        # content-disposition parsing fail.
        my ($filename) = $header{'Content-Disposition'}
                   =~/ filename=(("[^"]*")|([a-z\d!\#'\*\+,\.^_\`\{\}\
+|\~]*))/i;

    $filename ||= ''; # quench uninit variable warning

        $filename =~ s/^"([^"]*)"$/$1/;
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It is a bug in CGI::Simple

my ( $param ) = $unfold =~ m/form-data;\s+name="?([^\";]*)"?/;
      my ( $filename )
       = $unfold =~ m/name="?\Q$param\E"?;\s+filename="?([^\"]*)"?/;
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Example quoted string request

my $VAR1 = "POST http://localhost/cgi-bin/upload_quotes.pl\nContent-Le
+ngth: 138\nContent-Type:".
        " multipart/form-data; boundary=xYzZY\n\n--xYzZY\r\nContent-Di
+sposition: form".
        "-data; name=\"file\"; filename=\"stupid \\\"quoted\\\" filena
+me.txt\"\r\n-Content:".
        " stupid content\r\n\r\n\r\n--xYzZY--\r\n";
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I'd have suggested a regex, I've seen one many times, but I'm not up on the rfcs

http://tools.ietf.org/html/rfc1521

value := token / quoted-string
token  :=  1*<any (ASCII) CHAR except SPACE, CTLs,
                   or tspecials>

     tspecials :=  "(" / ")" / "<" / ">" / "@"
                /  "," / ";" / ":" / "\" / <">
                /  "/" / "[" / "]" / "?" / "="
               ; Must be in quoted-string,
               ; to use within parameter values
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http://tools.ietf.org/html/rfc2822#section-3.2.5

FWS             =       ([*WSP CRLF] 1*WSP) /   ; Folding white space
                        obs-FWS

ctext           =       NO-WS-CTL /     ; Non white space controls

                        %d33-39 /       ; The rest of the US-ASCII
                        %d42-91 /       ;  characters not including "(
+",
                        %d93-126        ;  ")", or "\"

ccontent        =       ctext / quoted-pair / comment

comment         =       "(" *([FWS] ccontent) [FWS] ")"

CFWS            =       *([FWS] comment) (([FWS] comment) / FWS)



qtext           =       NO-WS-CTL /     ; Non white space controls
 
                        %d33 /          ; The rest of the US-ASCII
                        %d35-91 /       ;  characters not including "\
+"
                        %d93-126        ;  or the quote character
 
qcontent        =       qtext / quoted-pair
 
quoted-string   =       [CFWS]
                        DQUOTE *([FWS] qcontent) [FWS] DQUOTE
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