Tnt

I made a concrete maker and I use an tnt dropper to to break the concrete and i use water and hoppers to collect everything. When the tnt drops it blows up about 20 blocks of concrete (1 piece of tnt). Then i went and check the collection system it only had 7 blocks in it. And I thought tnt was able to break every and no destroy anything anymore. Im not sure if this is a bug or not a feature yet.