@usr, your lens cover is most likely detected to be permanently open.

The culprit is the magnet - it's too bright. Remember the lens open detector is a simple light latch: a miniature LED and a photodetector. The area surrounding the whole assembly must be completely black in the lens closed state, otherwise it will generate enough reflection to trigger the detector and the phone will think the lens is open, as I have learned the hard way in this mod (see 4. Lens cover, part 1).

The solution is to use a black magnet. I used the flexible sheet from the back of fridge magnets. You can try colouring yours with a dollop of black paint or a black CD marker.