Blocks not falling at Y level 0

When placing scaffolding at Y level 0 with no blocks under them, they did not fall down. When placing scaffolding at Y level 1 they fell all the way down to the surface bellow.

 

Did not attempt this with other blocks effected by gravity. Did attempt in multiple locations.

 

While caving I was attempting to drop scaffolding down to climb down to a lower level without jumping. However the scaffolding was floating when I placed it at Y level 0.  Updating the blocks by placing more scaffolding or other blocks next to it did not effect it. The quick fix was to place blocks starting at Y level 1 or higher and they fell all the way down to the surface bellow that I was trying to reach.