The poster of the Ubuntu bug tells that the HPLIP PCL 5e driver (in his special case HPIJS via Foomatic/hpoijs-pcl5e) solves all his problems with Brother printers): short-edge duplex, duplex control via PostScript (-dDuplex, -dTumble) and a margin problem which he reported in another Ubuntu bug.
So we should perhaps look into the output of the HPLIP driver to make ljet4/ljet4d more universally working.
The poster of the Ubuntu bug tells that the HPLIP PCL 5e driver (in his special case HPIJS via Foomatic/ hpoijs- pcl5e) solves all his problems with Brother printers): short-edge duplex, duplex control via PostScript (-dDuplex, -dTumble) and a margin problem which he reported in another Ubuntu bug.
So we should perhaps look into the output of the HPLIP driver to make ljet4/ljet4d more universally working.