Are exporting from draft?
Can you give an example of your issue?
I know you can get lines on top of lines when you export to a dwg or dxf becasue your taking a 3D part and making it 2D. You also get some strange edges sometimes if you have draft or any kind of sloped surfaces that your importing.
Also, drilled/tapped holes give you multiple circles on dwg/dxf's as well?