Bad behavior of a redstone torch

What I expected to happen was...:

I excpected that the redstone on the block would be turned on.

What actually happened was...:

The redstone torch which I put on the side of a sandstone block had a weird behavior. If I put some redstone on the block and then I put a block on the redstone torch, it will make a clock which will be during a few second before turn off the torch, making the animation of water evaporating in the Nether.

Steps to Reproduce:
1. Put a redstone torch on a side of a block
2. Put some redstone on the block
3. Put a block on the redstone torch