Not to be picky but "PACKED array" here implies a multi-dim array which needs to be serialized to a file and reread back in proper order.
In many languages multiple dim arrays (vectors) are not always contiguous PACKED in memory.
So, attempting to use a bulk method of content read or write does not work very well in bin mode so using a CSV file seems to fix this.
I suppose one could force the first items of each line to indicate the index of the dims before issuing the final value.
Of course, this requires a known fixed dim argument which may not always be desirable.