If Daylight Sensors are in a dark room at night time they transmit a redstone signal

*What I expected to happen was:
I would cover a Daylight Sensor so it doesn't transmit any redstone signal. It worked perfectly at daytime.

*What happened:
When I tried the same thing at night time it transmited redstone signal.

*Steps To Reproduce:
1)Build a small room with no light source
2)Make a setup as show on the screenshots
3)Do /time set 15000