Description:
When a non full block moves by pistons it renders the width of the full block in one direction. This does occur for fence, walls (cobblestone wall, mossy cobblestone wall) , fence gate, stairs (changing orientation?), end rods. Maybe more blocks. This only occurs when the block is moving.

Examples
Fence post acting weird.mp4 (As a ingame example)

Test world:
MCPE-Fence post bug.mcworld