klucky

From MC-203063, which was marked as a duplicate 

I was building in the nether and was attacked by a ghast. It hit my build, which is constructed of nether brick and white concrete, and, to my surprise, the concrete broke. I looked at the minecraft wiki and as I suspected, the ghast's fireball (power of 1) should be weaker than concrete's blast resistance (b.r of 1.8), thus it should not have broken.

I then decided to test this with my friend, and we've come to the conclusion that when a fireball hits netherrack, a surrounding concrete block will break. It will, however, stay intact if the fireball hits the concrete instead, as expected. We filmed an example of our test, which I've attached (note there is no audio in the clip due to size limitations)

Steps to replicate this bug: 

1. Make a build using netherrack and concrete 

2. Entice a ghast to shoot a fireball at the netherrack in your build. Similarly, you can summon a fireball with commands 

3. The concrete will uncharacteristically break if the netherrack is hit 

Originally, I discovered this bug in a modded server, but I tested the bug in a vanilla single-player world and found the same results (1.16.3). Those findings can be seen in the attached video. 

In light of Spigot rendering the report invalid, I tested the bug as recommended in vanilla on a single player world (1.16.3) and found the same problem.

I've attached a video showing the issue below. Notice how in the first test, the fireball hits the netherrack behind the concrete, causing the concrete to break, but in the second test, the fireball hits the concrete directly, leaving the concrete intact.