Well today was definitely a fruitful day. I learned about C0/C1 control codes which were the reason for google to complain. I also realized where this stuff actually comes from (someone pasting a mis-encoded chunk of text into a browser window). Finally I know not to use is_utf8 anymore :)
Thank you for your comments.

P.S.How I ended up fixing this:
$_ =~ s/[\x{80}-\x{9F}]/\x{FFFD}/g;

[download]

In reply to Re^4: How to deal with malformed utf8 from XML parsing by ribasushi
in thread How to deal with malformed utf8 from XML parsing by ribasushi

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