Hi!
As Tobei had replied earlier, this is actually not a bug and it actually is a way for players with lower initiative to beat those with higher initiative. By playing your mystery at the right time, you can make the mystery more difficult to interrupt by reducing the amount of time a player has to react to it. This allows for players to utilize skill and strategy to beat people who have higher initiative or a prompt skill.
It is a part of the game and many players are using it, however, we do know it is of concern and Tobei has already forwarded it to the developing team!
Thank you!
~Jib