With

%fields = (
    __mpp    => [ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 ],
)
[download]

...
    my $self  = { %fields };
...
[download]

you only copy the reference and not the array itself. So all objects use the same array, which is not what you want. Consider using Storable::dclone to copy the default structure.