Looks like a bug in Perl to me. You can't used a tied variable inside of another tied variable's FETCH. I did some experimenting and came up with the following case that also illustrates the problem but with fewer moving parts inside the FETCH call:

#!/usr/bin/perl -w
package MyTie1;

sub TIEHASH { bless {}, shift; }

sub FETCH {
  my $self = shift;
  my $key = shift;
  return [{foo=>'bar'}];
}

package MyTie2;

sub TIEHASH {
    my $self= {};
    my %hash;
    $self->{hash}= \%hash;
    tie %hash, 'MyTie1';
    bless $self, shift;
}

sub FETCH {
  my $self = shift;
  my $key = shift;
  return [{val => $self->{hash}->{key}}];
}

package main;

my %hash;
tie %hash, 'MyTie2';
use Data::Dumper;
foreach my $user (@{$hash{one}}){
  print Data::Dumper->Dump([$user],['user']);
}
__END__
Can't use an undefined value as an ARRAY reference at refetch.pl line 
+33.
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I recommend you report this using the perlbug script that comes with Perl.

        - tye (but my friends call me "Tye")