The spinner seems to be just broken, at least in DB 2016-04-29.
@belly: Yes, 0 in the beauty pass should be the default. But denoising in a seperate pass offers more options. Not only that you can have one denoised and one non-denoised result but also one denoised with 0,5 and the other with 0,7 to without going through post(!). It should be up to the user´s liking and ... it should just work :)
Good Luck