QuickSort debugging in Matlab - algorithm

Question

I need help debugging QuickSort. As I was debugging, it actually sorts the array properly up to a point, but in the last couple of steps, it ends up doing unnecessary swaps and ends up returning an unsorted array. I've spent quite some time trying to figure out what's causing it, but I've made no progress.
I've chosen the partition as the first element (I know that's not optimal, but I'm just trying to understand QS).
Script:
A = [3 6 2 5 1 7 4];
rightIndex = length(A);
E = QuickSort(A,1,rightIndex);
QuickSort:
function [pvt, B] = QuickSort(A,left,right)
if left < right
[B, pvt] = PartnPivot1(A, left, right); %chosen pivot
QuickSort(B, left, pvt-1);
QuickSort(B, pvt+1, right);
end
Partition:
function [sortedSubArray, pivot] = PartnPivot1(subArray,leftIndex,rightIndex)
%% Initializations
S = subArray;
left = leftIndex;
right = rightIndex;
P = S(left); %pivot
i = left+1;
%% Partition
for j = i:right
if S(j) < P
temp1 = S(j); %
temp2 = S(i); % swap S(i) with S(j)
S(j) = temp2; %
S(i) = temp1; %
i = i+1; %increment i only when swap occurs
end
end
swap1 = S(left); %
swap2 = S(i-1); % final swap
S(left) = swap2; %
S(i-1) = swap1; %
sortedSubArray = S;
pivot = P;

Answer 1

The recursive calls to QuickSort need to assign the output to some variables, otherwise the sorted array never gets passed back. I also think you don't need to return the pivot.
I'm typing in a browser instead of testing in Matlab, but I think this will do it...
function A = QuickSort(A,left,right)
if left < right
[A, pvt] = PartnPivot1(A, left, right); %chosen pivot
A = QuickSort(A, left, pvt-1);
A = QuickSort(A, pvt+1, right);
end