Comment 61 for bug 1510344

Mario, as for the lock/idle problem is a different issue.

Things depend also on the hardware and how the kernel supports the notification of the kbd backlight changes, but if all is well supported this change should help:
https://code.launchpad.net/~3v1n0/unity-settings-daemon/keep-cached-kbd-backlight-updated/+merge/294662

It would be cool if you can try unity-settings-daemon with that patch.

Also, please provide logs when running
 gdbus monitor --system --dest org.freedesktop.UPower

And:
  udevadm monitor

While you use the keybindings to change the keyboard backlight and during a lock/idle/suspend cycle.