Oh, my god! The bug I haven't ever met happened in mine!

I went back to my house and was ready to go to bed when I heard the sound of skeleton.

Then I found that the skeleton WAS SPAWNED IN MY HOUSE! 

After beating the sleketon, I opened F3 to find the light level of spawner block and found it amazing to be greater than 7!(As the following picture shows) And it happens, I guess, with minimal probability.

I think it should be fixed to spawn a monster in a bright place, so please fix it.

Thanks