Adding random test cases found a weird frankenbug. Fixing backup seems to have fixed it. Do you have any good test cases ?

#!/usr/bin/perl -l

# http://perlmonks.org/?node_id=1144184

use strict;
use warnings;

sub e
  {
  my $p; 
  /\Gua/gc ? return e() : /\Gu/gc || return 0;
  1 while /\Gc/gc or
    ($p = pos(), /\Gb/gc && e() || (pos() = $p, 0)) or
    ($p = pos(), /\Gd/gc && e() && /\Gf/gc && e() || (pos() = $p, 0));
  return 1;
  }

for (qw( u udufu uau uu uc ubu ucbuc uaau ua uauau uccc uauuau
  udufuaua uaua uauau uccbucdc ))
  {
  print e() && /\G\z/gc ? "matches" : "   fail", "  $_";
  }
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