I don't get that.

$ perl -le'
>    $a=""; $a .= chr 1<<$_ for 0 .. 63;
>    print length $a;
>    $a = reverse $a;
>    print length $a;
> '
64
64
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Maybe it's cause I'm on a 32-bit build? $a contains 0..31,0..31 and the reverse once reversed.