Error with order by ; sorting main results by relation value

[mrelliot69]

I'm having a problem sorting the results with a column from my has_many relations;
Already check the code, and found something's that i don't understand,

Why the order_by variable is reseted on the loop if after the loop is where the result will be sorted using the sort function?
On the _build_sorter function how it works, because if the result have more than one position the arrayA will have multiples position, therefore the arraya[orderby] will not work, since is a multidimensional array