I've been having this problem for quite some time, but attribute it to a glitch in SW2010. With simple parts (extruded sketch), when I save the part as a .dxf file, the part is mirrored on either the x or y axis. Please see my attached screenshot and the part file. More of an annoyance then a problem. From searching on here, I see that this usually happens with sheet parts parts with the incorrect fixed face being chosen, but my parts are just flat faced w/o bends. Thanks!