Rookie mistake. Some films have micro-perforations built into them which release the steam at a specific rate. These types of film shouldn't be pierced as it will affect the heat transfer in the meal and you will end up with a meal which is undercooked. When you then just chuck it in for another minute, it loses excess moisture and you are left with a dry meal which is cooked unevenly.Just stab it with your steely knife, to let the steam out when heating, then after cut around film with said steely knife
(You can check out any time you want but you can never leave - Just sayin like.)