Weird textures of blocks when flying above clouds

When I made 16x16 square of TNT,I went high into the clouds and looked down.What happened is that there were some weird checkered textures.I made 16x16 square of oak planks,and then I saw a few,but big stripes.Also,if this is not a bug,feel free to tell me.
Note:I also added one more picture of TNT' where circles appear.