Hi treeshark, welcome to the monastery! :)

my guess is that here in your last sub addSomeNumbersFromSource

>

    my @array = $source{$data} ;
    return @array;
[download]

you rather need to flatten the array-ref to a list before assigning it to another array.

    my @array = @{ $source{$data} } ;
    return @array;
[download]

edit

otherwise @array = ( [  ... the-source-data ... ] ) has just one array-ref. (aka a "nested array" in your words)

whenever you have something like

@array = $scalar

that'll result into a one-element array.

... and $source{$data} is certainly a scalar, presumably holding an array-ref.