That snippet shows that yours is broken too. It doesn't return the last segment ("EN"). 
my $string = "RYOURPOSTBROKEN";

print("input:     $string\n");
print("expecting: R YOURPOSTBR OK EN\n");
print("\n");

{  #  mwah (split)
   my $re = qr/(?<=[KR])(?!P)/;
   my @arr = split $re, $string;
   print("split $re: @arr\n");
}

{  # tachyon-II (re)
   my $re = qr/(.*?[KR])(?!P)/s;
   my @arr = $string =~ /$re/g;
   print("$re: @arr\n");
}

{  # mwah (re)
   my $re = qr/[^KR]+.(?!P)/s;
   my @arr = $string =~ /$re/g;
   print("$re: @arr\n");
}

[download]
input:     RYOURPOSTBROKEN
expecting: R YOURPOSTBR OK EN

split (?-xism:(?<=[KR])(?!P)): R YOURPOSTBR OK EN
(?s-xim:(.*?[KR])(?!P)): R YOURPOSTBR OK
(?s-xim:[^KR]+.(?!P)): YOU POSTBR OK EN
(?s-xim:[^KR]*.(?!P)): R YOU POSTBR OK EN

[download]

In reply to Re^5: cleaving a sequence with specific alphabets by ikegami
in thread cleaving a sequence with specific alphabets by heidi

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