I prefer Google Calendar over Samsung's built in calendar app on the S4, for notifications. I don't need to remove the latter, and can't seem to; I just don't want it to display notifications. So I change the relevant settings, but periodically they revert.
I completely turn off notifications in S Calendar (no tone, no vibration), and turn them on in Google Calendar (with a specific sound and vibration and popup notification). In Google Calendar I also turn on "Show week number" and set "Week starts on" to Monday.
After some testing it seems these settings stay in place for as long as the device remains on. After turning it off and back on again, all of the settings in both S Calendar and Google Calendar, including the ones I mentioned not related to notifications, have reverted to their defaults (with notifications ON from S Calendar and OFF from Google) with the exception of the tone that I set for Google.
I'm fairly sure that having my phone turned off and then on again is exactly what happened each previous time I've noticed that my settings reverted.
I've looked at this post, and none of those solutions (for non-rooted phones) work; the settings still get reverted when I change them, and Samsung's calendar can't be turned off in Application Manager. If both calendars are having this issue I'm not even sure removing S Calendar would fix it.
A commenter on the first answer there seems to have the same issue, apparently since a recent upgrade. That may be the case for me too, because I bought this phone a year ago, but now both the device info and the app info for S Calendar have Android 4.4.
Why would these settings be reverting on every restart? How can I fix this, besides just not turning my phone off?