Just to double check (all though you marked that reproducibility is 100%), if you disable the do not disturb from the top menu, what happens? Does both of the icon disappear? When you enable again the do not disturb from the top menu settings does 2 icons re-appear?
Does reboot of the device do anything for this?
If you select 'Do not Disturb ’ mode using one button, the other changes colour and mimics it and vice-versa. If you remove the button using Settings / top menu, both disappear. If you reselect both reappear. Reboot makes no difference, I still have stereo buttons!
I tried restarting the home screen in settings/utilities to see if that would help and the second ‘Do not Disturb’ button has disappeared, but now I have two flashlight buttons instead.
I’ve just realized I had the same issue as you. I click on the setting button in the bottom right corner and “organize” item and deleted one “Flashlight”.
Can’t seem to reproduce it, but it happened to me ones, when I enabled the Android support button in Patchmanager. Then one more time when enabling all my patchmanager patches after latest OS update (4.5.0.19).
Isn’t it funny - you think that you’re the only one who has a bug like this because nobody else has raised the issue, so you report it as a bug and other users then say ‘Me too!’