HPGH -different colours different hights

Hello all,
I am currnetly using a piece of software from Lewetz in Germany which
takes a HPGL file and sends step an direction signals to Paralell
port.

In Corel draw I generate a drawing in 3 colours, assign the colours
to 3 pens and export it to HPGL.

It all works very well for just one pen but when I go to multiple
colours there is a fault where the Pen up and Pen down commands seem
to be mixed.

Has anyone else ran into this one??
are there any good HPGL optimisers out there.


Regards,
Bernard