When You /setblock ~ ~ ~ minecraft:piston_head Then Stand On The Piston Head On A Corner the other corner diagonally is invisible/missing its texture. See Screenshot For More Info On It.
To Reproduce
1.Go in a open space and Do /setblock ~ ~1 ~ minecraft:piston_head
2.Dont Destroy Any Blocks Around it or you will have to /setblock 206 56 20 minecraft:piston_head again
3.Stand on top of the head thing
4.Go To The Corner on top of the Head Thing
5.The Other Corner Side Will Be invisible/missing its texture
Piston heads are technical blocks and not intended to be used stand alone.