Yes it often happens, specially it happens at night when no light in room at all 
do these steps..
Open the Clock application > Press menu > Select Exit Bedside Mode if present (if you are NOT in bedside mode "Enter Bedside Mode" will appear).
if there is something wrong in your keys.. follow these steps,
Do this ON your device.
Go to Options > Status. On the keyboard type T E S T
There will not be a space to type the letters and you won't see anything entered, just type T E S T
Now, Click Menu > Start.
Check off ONLY the Misc test.
Click RUN
Click the trackball > NEXT.
Run the next test for backlighting and LED and you will see it working perfectly Inshallah! 
Like this if it really helped. 
No problem we are all here to help each other.
Mick just when you select the Enter bedside mode and again select the same option (it will show "Exit bedside mode") once done try a soft reset. Press Alt+ Crtl (two keys next after the space button) + del key. Once done you will see a slight difference in the backlight which is better than before.
Important thing is that you need to verify that these setting in Options > Screen/Keyboard > Backlight Timeout set to a time that you need and the Automatically dim backlight needs to be unchecked.
Tell me if that works.
Cheers!
Shazmin
