Falling sand / gravel disappears when falling on most "half" blocks

I placed a gravel block several blocks distance from the ground to fall on stairs. Despite falling "through" a torch, this worked without issues. However, when the stack reached to directly under the the previously placed torch, and the the point of the next block falling ONTO a torch, the newly placed blocks began disappearing.
This also applies to most other half blocks
*by falling, I mean being placed more than one block above the torch/sign/slab