Fence Blocks inhibit stacking of falling blocks (sand/gravel/etc.)

If you are to attempt to stack gravel/sand or any other type of 'falling block' on top of a fence post it will endlessly accept the block without actually stacking it it will create a single block that may contain several pieces of gravel without moving any other direction.

Upon breaking the fence post and allowing the gravel to fall all of the previously added pieces of gravel will fall out leaving just the original piece of gravel. 

-Video Attached