TNT ignores block hitboxes

So, I was making a TNT cannon, when I noticed that the front of the cannon kept exploding no matter how hard I tried to stop it from happening. I spammed F2 and in one of the screenshots, the TNT was completely ignoring block hitboxes. In another test, the TNT actually fell straight through a full block.

Update: TNT manages to clip through dispensers even in non-flowing water

Player cannons explode because of that