Backlit Keyboard not turning on when using the keyboard

[TheoL66]

As a preference, I have turned the backlit keyboard in the BIOS to turn off after 5 seconds.  It is my expectation that with this option, the keyboard will automatically light up if the keyboard is used, and the BIOS setting then results in the backlight turning off automatically after 5 seconds of inactivity.

However, when I use the keyboard, the backlight does not turn on automatically.  The only way I can get the backlit keyboard to turn on is to explicitly use the fn + F9 (which on my keyboard is the keyboard backlight toggle).  When doing so, it immediately turns off the backlight, regardless of keyboard activity. 

Is there an issue in the BIOS / Windows support - or is the only option to set the keyboard automatic turn off to "never" the only option?  

(If the latter, the "turn off backlight after ... " feature in BIOS is effectively useless, and certainly not the behaviour I want or expect).

[TheoL66 · Accepted solution]

Hmmm.  Looks like my misunderstanding of the "Automatic Keyboard Backlit" option.  If I uncheck this option, then the keyboard backlight behaves as I expect.  

That is - the keyboard backlight turns on when I use the keyboard, and turns off automatically after the period of inactivity specified in the "Backlit keyboard timeout".  (This option also has option "never" - which I do not use).

Can anyone explain the purpose of "Automatic Keyboard Backlit" option in the BIOS?