Torch Lighting

My problem is that 

I was playing mc and I was just exploring a cave and I placed 

torches in all over the cave....

Then after few days( in mc) when I again entered that cave 

the torch's lighting was completely changed 

The torch was just enlighting the block on which it was 

placed and the other blocks were not visible they were all pure black.... It also happens in my mining sites or underground...

Pls fix this bug...

THANK YOU