My clan has never used this trap, nor have we faced it before today.  The in-game descrption says:

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However, my clanmate that fought the team that had it said that in addition to the bombs at the beginning of the battle, Lydia put bombs on a Kalvalax (No Stoneskin) on a regular attack, and when his Leonardo put on Stoneskin from his passive, he got bombs.  Is there a bug with this trap?