Default Xperia Sola Screen never turns off .54 , speedy 5.5

I've strange issue.
I've Xperia Sola .54 UB, kernel Speedy 5.5 but this issue happens on every FW/kernel.
When I cover ambient light sensor (or when it's very dark in room) my screen never turns off. It's not proximity sensor. I've tried changing settings in display menu but my screen never turns off (for e.g. when it's in pocket).
When the light sensor is not covered everything is fine.
This problem is very annoying. When I forgot to press the lock button I wake up with week battery (about - 40% per night).
Maybe someone know solution.