DWG / DXF part output weirdness

Has anyone else had problems with DWG export from SW? (SW2003 SP3). I am exporting parts as DWG prior to adding extra information in ACAD and then
DXFing them for import to a Plasma cutter nesting programme. When I export to DWG, some of the parts seem to have: a. duplicate lines on top of each other b. some trimmed circles "invert" - tabs become notches, weld mouseholes become bumps etc.
This only appears to happen on some mirror components - the original ones are fine. I can't identify what triggers this and it only appears to happen on features with a radius of less than 30mm or so.
Any ideas?
Thanks in advance Deri
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Thanks - I'll get SP4 ASAP

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