Mouse Keys randomly enabled. How can I prevent this? I'm running macOS 10.12 on a MacBook Pro (Retina, 13-inch, Early 2015).

Randomly, mouse keys was enabled when my hands were not touching the keyboard. I don't have a bluetooth keyboard (although I do have a bluetooth mouse which I was not using at the time). This is the second time it has happened.

This is either a software or hardware bug, but it seems oddly specific to be a hardware bug when I don't see other random keypresses. 


How can I diagnose this? I can't find any mention of 'mouse' in system.log. 
Is this a known bug? I can't seem to find any other mentions.
Can I prevent this from happening again?
Default trigger switch for Mouse Keys is to hit  Opt ⌥   5 times.

You will usually hear the little 'zipper' noise it makes as it switches.

Occasionally, you can trigger it accidentally with seemingly unrelated presses of  Opt ⌥ . To reverse it, just tap it 5 times again.

To disable it entirely, System Prefs > Accessibility > Mouse &amp; Trackpad > Options... &amp; uncheck