I executed this sequence:
babel -ipdb az.pdb -omop az_opt.mop -xk "PM6" mopac az_opt.mop #this is an alias for MOPAC2016.exe babel -imopout az_opt.out -ipdb az_opt.pdb
The last command terminates with segmentation fault.
I used babel 2.3.2, MOPAC2016 under Debian Stretch. az.pdb is attached to this message.