I have noticed that whenever I ice smooth a wedding cake with an Italian meringue buttercream, once chilled, the cake sometimes develops hairline cracks that start from the bottom of the sides and start to travel upwards. The cakes rest on a very sturdy board, so they do not bend or sag. When I use an all-yolk or whole egg buttercream, I do not encounter this problem. The cakes were not frozen but I had assembled them the day before. This puzzles me. Any clues or suggestions?