Redstone lamp malfunction

What I expected to happen was...:It becomes completely dark and the illuminance becomes 0.

What actually happened was...:Partially brighter

Steps to Reproduce:
1. Set the time to midnight (Redstone lamp is bright)
2. Press the switch to dim the redstone lamp
3. Normally it will be pitch black, but it will be partially bright

※Reloading the world will fix it

    There is no lighting in the vicinity

The first photo is when everything is lit

The second photo is when everything is off but somehow bright

The third photo is after reloading the world