Glitched Blocks

When I break a block, the block that was behind it will show that it's stone, then once I've broken it (or place a torch on it) it will show what the block really was.

I expected for the block not to change after I either broke it or place a torch on it. (It gets more common the further down you get)

What actually happened was that the block SOMETIMES changed when I either put a torch onto it or break it.

Steps to Reproduce:
1. Get as far down as you can.
2. Then, try to find a block that changes if you put a torch onto it. (Sorry but it's quite random, so don't expect it to happen straight away.)