Arcs shifting when plotting to Oce

We've got an Oce TSD600 plotter that is exhibiting a strange problem when
plotting joined arcs. When drafting curbs for siteplans in AutoCAD 2005, for
instance, we use polylines. They are usually long, sweeping curves made up
of arcs and straight line segments. We're finding that when plotting to the
Oce, a few of the arc segments will shift up or down away from their
neighboring segments, resulting in a gap at each end of the segment.

We've tried exploding the polylines, re-creating them using new arcs,
switching from lightweight to heavy polylines, changing pen weights, etc.
Nothing seems to work.

Any input greatly appreciated.
Thanks...
Gary