I am getting more and more calls on this issue. I’m not sure if this is exclusive to Civil 3D yet. The only calls I have received so far is that this issue is in Civil 3D.
When switching from Paper Space to Model Space, the UCS will rotate by itself. This also happens when you save, get out of the drawing and then open it back up.
This seems to only happen when there is a saved view in the drawing. Others might experience it without having a saved view. I had this happen to me the other day. I unknowingly had a saved view in the drawing, which I never used, and this issue happened.
1. Delete the saved view(s), save drawing, close, re-open.
2. Go to the View tab, switch to Top view, save, close, re-open.