So how to dupe a candle:
1. Place a cake
2. Place a candle to the top of the cake
3. Place a candle on the cake again
4. Candle duped
BUG: You place the secound candle on the cake and it will break, but it will not get removed from the player's inventory, so there's the breaked candle and the candle in the player's inventory
This is being tracked in MC-203568