This is clearly a bug; however, all of the other reports have been given a vanilla "go to system preferences > keyboard > ..." answer or blamed on 3rd party software.
To substantiate the "bug" claim and refute any outside influence, today I:
- Booted into the macOS Sierra installer
- Erased the SSD
- Reinstalled macOS Sierra
- Completed the basic setup steps to get to the desktop
- Applied available OS updates through the app store
- Rebooted
- Used System Preferences > Keyboard > Modifier Keys to set the caps lock key to "No Action"
- Exited system preferences and verified the caps lock key was disabled
- Rebooted
- Tapped the caps lock key => light came on
- Used System Preferences > Keyboard > Modifier Keys to verify the caps lock key was again mapped to "Caps Lock"
- Rebooted into safe mode
- Repeated steps 7 through 11 (same result)
- Used System Preferences > Keyboard > Modifier Keys to set the caps lock key to "Escape"
- Rebooted
- Used System Preferences > Keyboard > Modifier Keys to verify the caps lock key was still mapped to "Escape"
- Rebooted
- Repeated steps 7 through 11 (same result)
The dialog is there, and this is obviously an intended feature. It doesn't work as intended, i.e. the changes do not persist through a reboot if the "No Action" option is selected, and is therefore a bug.
Now I have to go through all the other system settings I automate through my normal initial configuration script to see if any of those are getting reset to defaults without my knowledge. #Bunk