dwf problem : circles appear!!!

hi.
this is driving me crazy:
so much trouble with the dwf-format!
i started to deliver our projects in dwf due to security.
i didnt want people to have the original drawing with all
possibilities to change it.
but:

on the dwf in volo view (and the paper printed from here) appear big
circles out of nowhere!

the circles arent there in the plotpreview and not if i print dirctly
to the printer.
they have to do with the topography-polylines which consist in arcs
and circles.
all drawings whith these polylines have this problem. exploding them
didnt help. the only way i found to get rid of them is writing them to
DXB and reimporting them. but thats quite a lot of work for the number
of drawings i have...

does anyone know this problem? or even a solution?
is there at least an easier way to explode arcs to lines?

 

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