Hi jna, thanks for mentioning that, that can help some others in the future.

When that welding option is checked, the OBJ file that is created will be more complex in a certain sense because it will have faces that share a single 3d vertex, but have unique entries for uv and vertex normal for each face.

Some programs don't allow faces to carry independent information on them like this. So when they see "per-face" information they have to do something to try and reorganize it.

Welding turned off basically avoids this situation - adjacent faces will either share all information in common (3d pt, uv coordinate, and normal), or none instead of partial sharing.

- Michael