This is likely related to this change in 5.6 (from perldelta):

=head2 delete(), each(), values() and hash iteration are faster

The hash values returned by delete(), each(), values() and hashes in a
list context are the actual values in the hash, instead of copies.
This results in significantly better performance, because it eliminate
+s
needless copying in most situations.
[download]

Previously, only copies were used, which meant that foreach-aliasing didn't really alias into the real hash values:

my %hash = (name => 'andrew', beer => 'Ale');
foreach my $KV (%hash) {
    print ">>$KV<<\n";
    $hash{$KV} = 'Dark Ale' if $KV eq 'beer';
}
__END__
# with 5.00503:
>>name<<
>>andrew<<
>>beer<<
>>Ale<<

# with 5.6.1
>>beer<<
>>Dark Ale<<
>>name<<
>>andrew<<
[download]

As you can see, with 5.005, even after we've changed the value for the key 'beer', we still get the old value because it was a copy. In 5.6 we get the new value because it is an alias into the hash. Now, in your situation, after deleting the key '*test' the next iteration involves an alias to a non-existing value and this is causing a problem for perl (which with -w gives "attempt to free unreferenced scalar", and a segfault otherwise).