Skuntank is receiving errata for its "Evolutionary Gas" Poké-Power. Evolutionary Gas's effect ends when the Defending Pokémon is no longer the opponent's Active Pokémon. The correct card text should read, "Once during your turn (before your attack), when you play Skuntank from your hand to evolve 1 of your Active Pokémon, you may choose 1 of the Defending Pokémon. If that Pokémon tries to attack during your opponent's next turn, that attack does nothing. (If the Defending Pokémon is no longer your opponent's Active Pokémon, this effect ends.)"
Source: Organized Play News (2009-02-26)