I've run your code on the cygwin Perl v5.8.7 built for cygwin-thread-multi-64int on Windows XP Pro with similar results. I've also tried fiddling with the config parameters, all to no avail.
Looking at the documentation I get suspicious since basically there's practically none. The code is implemented in C and frankly, I don't feel like going through it now.
I'd recommend you submit a bug report to the author of Text::ExtractWords and meanwhile resort to some other module like cpan:/String::Tokenizer if that's fast enough for you.
Hope this helps, -gjb-