I get the same behavior on linux. I'll let Alex know.

I traced this bug
to the fact that mouse interaction mode used in Base\GUI\vtkSlicerViewerInteractorStyle is stored in vtkMRMLSelectionNode and if there is no such node in the scene the interaction was undefined.

I fixed it by setting the default mouse interaction in vtkSlicerViewerInteractorStyle to vtkMRMLSelectionNode::MouseTransform in this case, I hope it does not break anything else.

I am wondering if the vtkMRMLSelectionNode is right place to store that kind of information and if vtkSlicerViewerInteractorStyle the right place for adding fiducial. Another way of adding fiducials would be to invoke mouse events from vtkSlicerViewerInteractorStyle and for Fiducial module (or Logic) to observe them and create fiducials then.

Changing status from "confirmed" to "closed."