You don't show any code, and from your description, it's not exactly clear to me what you have. I interpret your description as something like the following:

tie my @in, 'Tie::File', $filename;
tie my @mem, 'Tie::Array::Packed', ...;

@mem = @in; # sluuuurp

print "@in";
[download]

And your claim is that the output from print is not what you expect.

Can you provide us with self-contained (small) code and (small) data that reproduces the problem?