How do I completely disable automatic keyboard backlighting on Macbook Pro with OSX Lion?

Lab Tick is a shareware menu item that gives you complete control over the keyboard backlight. You can set the level of illumination by hand, and electively disable automatic adjustments made by the OS.

You can try reset SMC to fix the bug. Shut down the computer,then press option+control+shift+Power for several seconds and then boot it.

I had this exact problem you described on my MacBook Pro with macOS Sierra. What I did to solve it was:

1. Open Keyboard preferences: Apple Logo > System Preferences > Keyboard
2. Check and uncheck the top 3 options ("Adjust keyboard bright in low light", "Turn keyboard backlight off after X of inactivity", and "Show keyboard and emoji viewers in menu bar". I just messed around with them to see what they do.
3. Close it out.
4. Re-open Keyboard preferences: Apple Logo > System Preferences > Keyboard
5. Make sure "Adjust keyboard brightness in low light" is unchecked.
6. Close it out.
7. Reboot.

I'm not sure if all these steps are necessary since I cannot replicate the initial problem anymore, but I found the reboot to be necessary. Good luck.