Falling Blocks break by themselves

As you can see in the image, every falling blocks can break without any reason. I think it occurs because a block pass through another one. So when one of them is no longer an entity, but becomes a solid block, the other can't be placed (we can see it at the level of the piston).

 

I'm using a tower of concrete powder, paired with a piston activated each 4 ticks to illustrate that bug.