Tile mysteriously changes during game – Hong Kong Style Mahjong Review

Fun game but my tile changes mysteriously during the game. For example, I got a chow of 5,6,7 sticks and then my 8 character tile in my hand changed to a stick card. I forgot what number though. I was hoping to win the game by getting a chow with my 7,8 character tiles but after the 8 changed, I had to change my strategy.
Review by Ngaialator on Hong Kong Style Mahjong.