You will see that the output will flicker when you move around (sometimes you need to click in the editor, do something. Other times, it updates the image even when live nodes are disabled).
If you use a constant instead of a param for Radius, this does not occur.
In the process of retesting this issue for you. I feel like I missed the version number and this may not have been corrected until 4.12, in either case as soon as I am done I will respond back here for you.