if a VSTi provides no GUI, the host/Renoise provides a standard gui with sliders. If you move the window to the very right of the screen, on a huge resolution, close it, save the song, and later open the song on a lower resolution, the window will be stick on the right border, and also not draggable to the middle. Since the dragging area around the close button seems not to be reacting on mouse action. So you will have to change the resolution just to make the window draggable.