The bug

If an in-game control is bound to the POWER key (numeric ID 222 in options.txt) in 1.12.2 or a prior version (likely in conjunction with the system settings being configured such that the system does not shut down when the button is pressed), and then a newer version is loaded, that control will be set to "Not Bound".

It is possible to bind controls to this key in modern versions, in which it displays as "scancode.350" (see MC-170376), leading me to believe that the control becoming unbound is not intended, although the fix for this should preferably include a fix to MC-170376 for at least this specific button.

How to reproduce

It no longer appears to be possible to bind this control to keys in 1.12.2 or earlier - this may be a LWJGL or operating system issue, so unlike in MC-265731 and MC-265853 we'll have to force this by modifying options.txt.

1. Load up version 1.12.2 or earlier
2. Find options.txt in .minecraft
3. Change one of the numbers after a keybind to 222
4. Load up 1.12.2 or earlier
5. Check your key binds menu
6. Load up the latest supported version in that same profile
7. Check your key binds menu again

Expected results

The control that was bound to "POWER" would automatically be converted over to a key named something along the lines of "Power".

Actual results

That control now says "Not Bound".

How to fix

Have old options.txt files which bind a key to 222 convert this over to scancode.350 (or preferably an actually named key ID which replaces this, as to permit compatibility across operating systems) instead of key.keyboard.unknown.