Merge sorting, arrays rearranging during merge. Java

Question

Im having some trouble with my arrays with merge sorting. Every case I have, the merge works fine until it hits the recursive method and send a previously merged array back. Most cases it rearranges the arrays that were already sorted and messes up the second merge method. For example: (3)(2)(1)(4) -> (2,3)(1,4) -> (1,3,2,4) would be a probable result. What am I doing wrong that could be causing this?

public static int[] mergeSort(int[] numbers) {

     if (numbers.length == 1) {
       return numbers; }

     int[] leftSide = new int[numbers.length/2];
     int[] rightSide = new int[numbers.length-leftSide.length];

     System.arraycopy(numbers,0,leftSide,0,leftSide.length);
     System.arraycopy(numbers,leftSide.length,rightSide,0,rightSide.length);

     mergeSort(leftSide);
     mergeSort(rightSide);

     displayArray(leftSide);
     displayArray(rightSide);

     numbers = merge(leftSide,rightSide);

     System.out.println("=============");

     return numbers;
   }  

 public static int[] merge(int[] left, int[] right) {

     int[] temp = new int[left.length+right.length];

     int l = 0;
     int r = 0;
     int t = 0;

     while (l < left.length && r < right.length) {
       if (left[l] > right[r]) {
         temp[t] = right[r];
         r++;
         t++; }
       else {
         temp[t] = left[l];
         l++; 
         t++; }
     }//while

     while (l < left.length) {
       temp[t] = left[l];
         l++;
         t++; }
     while (r < right.length) {
         temp[t] = right[r];
         r++; 
         t++; }

     displayArray(temp);

     return temp;
   }

Answer 1

The mergeSort function returns a sorted array, which we are not tracking. Since the sorted array(left & right) is lost, the merge function is again picking up unsorted left and right array. The fix would be to update

mergeSort(leftSide);
mergeSort(rightSide);

to

leftSide = mergeSort(leftSide);
rightSide = mergeSort(rightSide);

This will update them to their respective sorted values