Actually we tracked down the address of the global controller before and after co-processing, and we can see it changing, so it seems VTK is replacing the global controller with another one (probably an MPI one).
Regarding IceT: is there any way of not relying on IceT for compositing? We are trying to implement a non-MPI communicator so it’s going to be pretty limiting if IceT forces us to have MPI.