How does selectGPU work in MDCE?

I have 4 workers and 2 GPUs (set the "compute mode" to be "default") in my PC. When I use the "local" cluster profile (the path of "selectGPU" is added) to run several tasks (say 4), they only use the first GPU but leave the second one in idle. It seems the function selectGPU does not work in this condition.

However if I type the following codes in the command window:

spmd
  gd = gpuDevice;
  idx = gd.Index;
  disp(['Using GPU ',num2str(idx)]);
end

the outputs are:

Starting parallel pool (parpool) using the 'local' profile ... connected to 4 workers.
Lab 1: 
Using GPU 1
Lab 3: 
Using GPU 1
Lab 2: 
Using GPU 2
Lab 4: 
Using GPU 2

which reveal that the function selectGPU does work in this spmd condition.

So I am wondering how does selectGPU work? Can I make it work in MDCE?