...Liked the regex; not so much, lines 15 and 16...
so tried 5.012 which didn't like 16 either.

So left the regex alone and re-wrote Lines 15-16 (much more verbosely) to work nicely with 5.12:

#!/usr/bin/perl
use Modern::Perl;

# 934820

my $palindrome_re = qr{
    \b
    (?<pal>          # A palindrome is a sandwich...
        (?<char>\w)  # starting with white bread...
        (?:          # filled with either...
            \w?      #   peanut butter (maybe)...
        |            # or...
            (?&pal)  #   another sandwich...
        )
        \k<char>     # topped off with white bread!
    )
    \b
}ix;

my @Rev_arr = qw /Research tattarrattat Kanakanak Qaanaaq Foobarblivit
+z/;
for my $word(@Rev_arr) {
     if ($word =~ /$palindrome_re/) { 
        say $word; 
     } else {
        say "$word is NOT a palindrome";
    }
}
[download]

Execution:

C:\>934820.pl
Research is NOT a palindrome
tattarrattat
Kanakanak
Qaanaaq
Foobarblivitz is NOT a palindrome

C:\>
[download]