[vtkusers] Can't interact with BorderWidget after specifying position coordinates

[David Doria]

I am trying to initialize my border widget by specifying one of the
corners with:

  vtkCoordinate* lowerLeftCoordinate = static_cast<vtkBorderRepresentation*>(
      this->BorderWidget->GetRepresentation())->GetPositionCoordinate();
  lowerLeftCoordinate->SetCoordinateSystemToWorld();
  lowerLeftCoordinate->SetValue(0,0,0);

However, once I do that, I can no longer interactively move the lower
left corner of the BorderWidget/Representation. Is there a way to
specify this position without "locking" it?

(Here is an example: http://codepad.org/YudrwAGm)

Thanks,

David