The items in your array are in insertion order, so what remains is each individual hash. In your example above, you have a list with one element: a standard hashref. Since you can't "tie" an anonymous reference like this, you would need to use the object-oriented abilities of Tie::IxHash instead:

use Tie::IxHash;

push @data, Tie::IxHash->new( yo => mama, bliz => at );
push @data, Tie::IxHash->new( one => two, three => four);

print join(", ", keys %{$data[1]});  # one, three
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