In stead of: 
my @chars = split( //, $in );
foreach my $char (@chars) {
   $check += ord($char);
}

[download]
You could use: 
$check += ord $_ for split //, $in;

[download]
But to your question, I don't know. I think I read an explanation once by Dominus, on the mailing list to his superb book Higher Order Perl (which I highly recomend!)

Edit: In light of BrowserUk's response below, it's unlikely that this is related to the explanation I mentioned above. Sorry for confusing...

In reply to Re: Weird behaviour with match-time code evaluation and backtracking by stiller
in thread Weird behaviour with match-time code evaluation and backtracking by moensch

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