What I expected to happen was for redstone alternative adventure maps with invisible signs to work as they should.
What actually happened was the invisible signs would crash the game as there are no actual entities there.
Steps to Reproduce:
1. Place some signs on top of signs in a world.
2. Delete the entities file using iExplorer or any other software.
3. Go back into the world and destroy the bottom/first placed sign.
4. The game will crash.
Duplicate of MCPE-1592