Why the optimization variables is same on each processor when using parallel optimization toolbox?

Hi, I am a beginner of parallel optimization.

I used the testing code from Minimizing an Expensive Optimization Problem Using Parallel Computing Toolbox, and made a slight change to monitor the optimization variables of each processor(see below).

function f = expensive_objfun(x)
%EXPENSIVE_OBJFUN An expensive objective function used in optimparfor example.

%   Copyright 2007-2013 The MathWorks, Inc.

%% display processor and optimization variables 
task=getCurrentTask;
if isempty(task)
    taskid='~';
else
    taskid=num2str(task.ID);
end
disp(['Task' taskid  char(9) 'x: ' num2str(x)])

%% objfcn from MathWorks
% Simulate an expensive function by pausing
pause(0.1)
% Evaluate objective function
f = exp(x(1)) * (4*x(3)^2 + 2*x(4)^2 + 4*x(1)*x(2) + 2*x(2) + 1);

The command window shows optimization variable of each iteration on each processor, and what surprised me is the variables are totally same!

Task~	x: -1  1  1 -1
Task1	x: -1           1           1          -1
Task2	x: -1           1           1          -1
Task3	x: -1           1           1          -1
Task4	x: -1           1           1          -1
Task~	x: -4.2359      2.4679     -1.5394     0.80007
Task~	x: -2.6179      1.7339    -0.26972   -0.099966
Task1	x: -2.6179      1.7339    -0.26972   -0.099966
Task2	x: -2.6179      1.7339    -0.26972   -0.099966
Task4	x: -2.6179      1.7339    -0.26972   -0.099966
Task3	x: -2.6179      1.7339    -0.26972   -0.099966
Task~	x: -2.3713      2.3761     0.40751     0.35945
Task1	x: -2.3713      2.3761     0.40751     0.35945
Task2	x: -2.3713      2.3761     0.40751     0.35945
Task3	x: -2.3713      2.3761     0.40751     0.35945
Task4	x: -2.3713      2.3761     0.40751     0.35945
Task~	x: -1.5812       3.273     0.18625     0.43047
Task1	x: -1.5812       3.273     0.18625     0.43047
Task2	x: -1.5812       3.273     0.18625     0.43047
Task3	x: -1.5812       3.273     0.18625     0.43047
Task4	x: -1.5812       3.273     0.18625     0.43047
Task~	x: 2.07788      11.3179      1.36175      1.16423
Task~	x: 0.24833      7.2955       0.774     0.79735
Task~	x: -0.66645      5.2842     0.48013     0.61391
Task~	x: -1.1238      4.2786     0.33319     0.52219
Task1	x: -1.1238      4.2786     0.33319     0.52219
Task2	x: -1.1238      4.2786     0.33319     0.52219
Task4	x: -1.1238      4.2786     0.33319     0.52219
Task3	x: -1.1238      4.2786     0.33319     0.52219
Task~	x: -1.3194      4.9367     0.32417     0.27363
Task1	x: -1.3194      4.9367     0.32417     0.27363
Task2	x: -1.3194      4.9367     0.32417     0.27363
Task3	x: -1.3194      4.9367     0.32417     0.27363
Task4	x: -1.3194      4.9367     0.32417     0.27363
Task~	x: -1.4612      7.2753     0.13652    -0.23738
Task1	x: -1.4612      7.2753     0.13652    -0.23738
Task2	x: -1.4612      7.2753     0.13652    -0.23738
Task3	x: -1.4612      7.2753     0.13652    -0.23738
Task4	x: -1.4612      7.2753     0.13652    -0.23738

Could anyone please tell me why, thanks very much!