Redstone Lamp powered, no change in light level

We powered the redstone lamps directly via a daylight sensor on them which are inverted so that they start to emit light when the night is starting.

• => Light sensor
  x => Redstone Lamp

sometimes redstone lamps will not emit light. But they will change the texture into the texture of lamps which are powered by energy from the light sensor.

So enemy mops are going to spawn while they should not be able to because there must be enough light in this area because there is a redstone lamp that is powered by a daylight sensor...