Steps to reproduce:
1. Set 2D view in scene view
2. Close Unity
3. Delete Libraries and Project settings of any project folder
4. Open said Project
5. The grid will be vertical instead of horizontal even though view is set to 3D

Expected: Either 2D or 3D view grid is visible, not an inbetween
Actual: grid is shown as if 2D was enabled, but you can view and move around in 3D

Note: Doesn't reproduce post 2017.1.0f3 so just reported that there would be a case for dupes.