Some Light Manipulator handles behave in a way that makes it difficult to control them once a light has been scaled.
Steps to reproduce:
Create a GafferThree node
Create a light and assign to it the KatanaSpotlight shader to get more available manipulators.
Select the light in the Viewer and choose Cone Angle under Manipulators.
Select the manipulator handles and try modifying the Inner Angle or Outer Angle. You will see the transition is smooth and you can set them to the desired position easily.
NOW scale the light using the manipulator if available, if not the transform.scale parameter under the light object transform options. Scale to something like 50x50x50.
Try changing the inner/outer angle again and you can now see that the changes are jaggy and not smooth. The mouse doesn't appear to match the handle position and when changing, there is a sudden jump in position, the handles working at 5 time the movement speed compared to before. This will make it difficult to accurately set the manipulator's handled.