In the editor, when placing blocks by holding down the mouse, then using Z or C to move up or down, when there is a lag spike, it leaves gaps in walls and things when building...
The game just doesnt have enough processing power and framerate to place every block. the only way of combatting this is to imagine the pillar like a line, and if the user is pressing a key for x time, it fills between the two ends, kind of like an auto filler.