View > Soft Proofing has no influence, if softproofing is changed in Image > Properties dialog, that color mode is turned on no matter the View toggle. Also can't switch off 'store softproofing configuration in the image', when you toggle it off and press OK, if you open the image properties panel again, it's still on.
I cannot reproduce the first on KDE Neon 16.04, there must be something more going on here. And I have the opposite with the store softproofing toggle, I cannot turn it on.
Maybe it got to do with the settings coming from Krita v3 (in case of the toggle). For the first part of the issue (softproofing always on), in v3 I also played with softproofing in Settings > Configure Krita, maybe it's connected to that somehow. I use CTRL+Y (in v3) to check my values so I set the softproofing to grayscale in settings so I don't have to change per image in Image > Properties each time.