WHIZARD GenCrossSection error message

WHIZARD: activating the writing of the cross section to the HepMC event record leads to the error message:
WARNING::GenCrossSection::to_string: the number of cross-sections cross_sections.size()=1 does not match the number of weights0
not reproduced by Juergen Reuter in standalone mode. Need to check versions of Whizard and HEPMC to solve the problem.

Start by reproducing the WHIZARD configuration that writes the cross section to the HepMC event record and capture the full warning. Compare the WHIZARD and HepMC versions with the standalone case reported by Juergen Reuter; done means identifying the version or configuration mismatch and documenting the confirmed resolution.

Written by the indexing model from the issue text.