The ones that have "downward pointing" normals were probably created by mirroring other ones, when mirrored the kind of natural local z axis for a circle gets flipped around, that's probably why some happen to be pointing downwards. It's not supposed to make any difference, but these programs that are having problems most likely have a bug in their implementation of the DXF "arbitrary axis algorithm" where they're not generating the coordinate system for downward pointing extrusion vectors properly. The arbitrary axis algorithm needs special case handling when the extrusion direction is colinear in any way with the world z axis, and they're probably only handling the special case when it's in the same direction as world z.

- Michael