Put the summary of the bug you're having here

when i try to place a sign on top of a sign it doesn't place but sometimes will (not very often).

What I expected to happen was...:
when i placed the sign on top of the sign i expected it to place a sign on top of a sign not just sign on block

What actually happened was...:
i placed the sign and i could not place another sign on top of it.

Steps to Reproduce:
1. place a sign
2. try to place a sign on top of the sign you just placed (not in your inventory but on the sign you placed on the block) .

3.the signs should be stacked on top of each other.