Put the summary of the bug you're having here

What I expected to happen was...:
I thought that it would be the same with or without the block above the torch.

What actually happened was...:
It didn't light without the extra block but did with it.

Steps to Reproduce:
1. Place a redstone torch with a random non-tnt block next to it, and above the non-tnt block put a tnt block, an then destroy the non-tnt block
2. Observe that the tnt has not exploded
3.  Put another non-tnt block above the redstone torch and next to the tnt block and the tnt should light.