The bug

When placing command blocks in certain quadrants of the world, facing a particular direction makes the blocks harder to place upwards. This does not happen with most other directional blocks.

How to reproduce

1. Create a new superflat world
2. Begin flying in creative mode
3. /tp -5 6 5 90 80
4. Place a piston
   →  It's pointing up
5. Break it and place a command block
   →  It's pointing towards you
6. Back up five blocks, so your X coordinate is positive, then place another command block
   →  It's pointing up

Notes

Blocks that work correctly:

 Piston, dispenser, dropper, barrel, observer

Blocks that work incorrectly:

 Command block