Unusual merge sort error

I have an unusual problem. I am running a Merge Sort and come across the following: the method works correctly, except for the last pass. When using a random array Integeras input, an array is returned Integerwhere the first and second half are sorted separately. The merge works correctly, except for the last pass. After several hours of working with the debugger, I realized that the “reference point” always evaluates falseon the last pass, although it should not be based on values.

All help is appreciated.

public static Integer[] mergeSort(Integer[] input)
{
    if (input.length == 1) return input;

    int splittle = input.length / 2;

    Integer[] first = new Integer[splittle];
    Integer[] second = new Integer[input.length - splittle];

    for (int i = 0; i < splittle; i++)
        first[i] = input[i];
    for (int i = splittle; i < input.length; i++)
        second[i - splittle] = input[i];

    mergeSort(first);
    mergeSort(second);

    LinkedList<Integer> returner = new LinkedList<Integer>();

    PriorityQueue<Integer> sFirst = new PriorityQueue<Integer>();
    PriorityQueue<Integer> sSecond = new PriorityQueue<Integer>();

    for (int i = 0; i < first.length; i++)
        sFirst.offer(first[i]);
    for (int i = 0; i < second.length; i++)
        sSecond.offer(second[i]);

    // while (!sFirst.isEmpty()&&!sSecond.isEmpty())
    // returner.add((sFirst.peek()>=sSecond.peek() ?
    // sFirst.poll():sSecond.poll()));

    // expansion of line above for debugging purposes

    while (!sFirst.isEmpty() && !sSecond.isEmpty())
    {
        int temp = 0;

        if (sFirst.peek() >= sSecond.peek())
            temp = sFirst.poll(); // Mention point
        else
            temp = sSecond.poll();
        returner.add(temp);

    }

    while (!sFirst.isEmpty())
        returner.add(sFirst.poll());
    while (!sSecond.isEmpty())
        returner.add(sSecond.poll());

    return returner.toArray(new Integer[0]);
}