CKKW(L) merging with MG5aMC_PY8_interface

Hello

I try to run MG5 (v2.6.3.2) to simulate multijet events.
I define for simplicity qq->qq+jets production, and I run MG5 simulation using:

./bin/mg5_aMC jobOption.dat

where the jobOption.dat have next lines:

# Set up initial parameters
define j = g u u~
generate u u~ > u u~ @1
add process u u~ > u u~ j @2
add process u u~ > u u~ j j @3
output MultiJet_LO
launch
shower=Pythia8
detector=Delphes
analysis=ExRoot
# Modify run_card.dat
set nevents 10000 # number of unweighted events requested
set lhaid 280400 # using NNPDF3.0 at NLO PDFset from ATLAS
set ickkw 0 # 0 no matching, 1 MLM
set xqcut 0
set ktdurham 50 # Turn on to activate CKKW(L) merging with Pythia8
set ptj 50 # minimum pt for the jets
set drjj 0.4 # min distance between jets
set htjmin 1000 # minimum jet HT=Sum(jet pt) in GeV
set sys_pdf none # Dont run pdf systematics
set use_syst False # Dinable systematics studies
# Modify pythia8_card.dat (Here we introduce CKKW(L) merging instead of MLM)
set JetMatching:merge off # switch off MLM matching
set Merging:doKTMerging on # kT scale for merging shower products into jets
set Merging:nJetMax 2 # Maximal number of additional jets in the matrix element
set Merging:Process pp>jj # The string specifying the hard core process
set Merging:TMS 50 # The value of the merging scale
set Merging:Dparameter 0.4 # Definition of longitudinally invariant kT separation
set Merging:nQuarksMerge 4 # which quarks flavours are considered additional partons
done

The I end up with "Segmentation fault" from pythia8 run.

The reason that I see is :

Line461 of MG5aMC_PY8_interface.cc resets process string:
pythia.settings.word("Merging:process","guess");

when I run pythia8::next() command
it calls Merging::mergeProcess(process)
which calls MergingHooks():initOnProcess(process,particleDataPtr);
which tries to access the residual process by finding string after ">", and once it fails (since the sting is "guess") the program quit with segmentation fault error

if I comment L461, CKKW merging is executed w/o errors.

Is it the right thing to do, to keep the process name as it is or I should set up CKKW merging options in pythia card differently?

thanks in advance,
Michael