Comment 6 for bug 840462

Update:

The bug seams to be a problem with Unity 3D.

Using Unity 2D or Gnome Shell everything works fine: can use nvidia-settings to change, add, remove monitors on the fly. Also the use of disper is possible.

Addendum:

If I play arround with nvidia-settings (under Unity 3d) I can get twinview working the following way
- moving the screens (see attached screenshot) together
- apply settings
- move screens side by side
- apply
- move the smaller screen on top / on bootom
- apply

Overall performance of 3d with nvidia 280.13 is poor (e.g. lt-Tab switcher). That indeed is an indicator

 I am writing this under the Gnome-Shell environment, because Unity 3D is not usable for me (crashes, Alt-Tab not working, cannot get minimised windows back, performance really bad, ...).