Compiled script for parallel neural network training

When I run a script to train a neural network from within the MATLAB enviroment using Parallel Computing Toolbox, training is performed using parallel MEX workers. If I generate (using MATLAB Compiler) and run a standalone application from the exact same script, the training is performed in MATLAB calculation mode on a single worker.

In both cases the parallel pool is opened and closed by the script, so there is definitely a parallel pool open. The MATLAB documentation indicates that the relevant functionality from both the Neural Network Toolbox, as well as the Parallel Computing Toolbox, are available in Compiler. How do I get the training to occur in parallel, in a compiled script?

Update : I have found out that the issue described above occurs with R2017b, but not with R2018a. In the latter case all workers are fully utilised during training.