I cannot place a solid block on certain spots above ground where a creeper blew up. I'm guessing the game the empty space as if there was still a mob there, as i was fixing the drop chute for a spawner farm for creepers. A group of creepers were present at y coordinate 69 and one of them blew up and killed the rest of the creepers. Since then i could only place scaffolding and slabs to try and remedy the issue.  Note that i cannot make full blocks with slabs nore place them from the side of other slabs.