2D Light question

I'm having a problem with 2d lights. I've made a normal map for my tileset, and its working fine.

You can see that the lights just affect the left corner, as expected. [1]

But this not happens when I enable the ground layer to be affected by light.

It seems that the light is passing by under the obstacle and reaching the other side. How can I change this, to the light be blocked by the obstacle? (I'm using tilemaps)