Hey there. I'll just assume you're using a stock rom, and I'll asume it (your light sensor) is actually broken.
"Repairing" it wont be cheap, because it's part of the flex ribbon/cable assembly, which also holds the front camera, notification LED, proximity sensor, home button, display/touchscreen assembly connector and speaker pins. Pretty much everything is soldered to this component.
There *could* be a problem with your flex ribbon. Perhams some of its wires are starting to break? I know this can lead to all sorts of issues, because it started messing with my LED some months ago. But, on the other hand, it might just be a faulty sensor.
Whatever it might be, I say you leave it as it is. Replacing the flex is no joke on the XMP.
CyanogenMod-loving Xperia Mini Pro user.