Annoying, isn't it? Perl has its own idea of whether your data should be treated as UTF8 or as 8-bit encoding, and it may not agree with your idea. If you concat a plain 8-bit string with a string marked as UTF-8, Perl will convert the 8-bit string to UTF-8 as well, whether you want it or not.

The trickery is all connected to the UTF8 flag, which is a bit flag attached to each string. For the data that XML::Parser returns, that UTF8 flag is set.

To get rid of this behaviour, clear the UTF8 flag. One way you can do it, is like this:

sub de_utf8 {
    use bytes;
    return "$_[0]";
}
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This way, the resulting string will be the same byte data as the original string, but with the UTF8 flag cleared. So now, the string should stay in ISO-Latin-1.