I might be responsible for that optimization. I made some modifications to the regex engine a couple years ago involving skipping non-pattern parts of regexes when looking to optimize. So, how can can you defeat it? Well, you could wrap the 'XXX' inside a (??{ ... }). 
$rx = qr/.../;
" failed " =~ /(?{ $ok = 1 })(??{ $rx })/;
print "OK = $ok\n";

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Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart

In reply to Re: Disabling regexp optimizations? by japhy
in thread Disabling regexp optimizations? by diotalevi

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