World generation cutted off by... Flying dirt?!!

I created a world to test the snapshot and suddenly chunk generation started to slow down. So I decided to go and see why world was not being generated. While testing a lot of things I placed a dirt block at the generation border and suddenly a line of flying dirt blocks appeared surrounding the generated chunks of the world.

In my opinion, the problem was getting the block placed instead of getting the error message "You can't place blocks outside the world"