Feature Line Offsets as Polyline

We have something weird going on with one of our users that isn't happening with others. When he offsets a feature line, sometimes it offsets as a polyline. If he audits, purges, saves and closes Civil 3D completely, it works for a while when he gets back into the file. I can offset the same line on my computer with no problems. Anyone have any ideas why this is happening? Any help is appreciated.

Thanks,
Desi

Let us know if you figure out how it happened, it could be useful. To do that now I'd have to offset, set all the elevations to 0, then explode.