Summary:
Non full blocks like fence, fence-gate, stairs, doors, levers, pistons (only the "body"), flowers, etc can appear invisible to the player when there is no block placed in the (sub)chunk.
They remain invisible until the chunk receives a (block) update.

Steps to reproduce:
Single player, Creative, 1.2.10.1
1. Make sure there is a empty subchunk (with a clear sky). For example let the player stand at Y64 and remove any block, flower, grass, etc in that area (chunk) that is >=Y64.
2. Now place a block at Y64 and remove the block. (i used a grass block)
3. Place one of the non-full blocks in the exact spot as the just removed block.
4. Notice that the non-full block placed is invisible in that chunk and all other non full blocks that are placed (in that subchunk). Until it receives a update (by using a full block).

Video attached:
Invisible non-full blocks.mp4

Additional notes:
If step 4 doesn't work, reload the world and try again from step 1 for the same area. Or try 16 blocks higher (80,96 etc).