I use Sharon Z's crusting buttercream on my wedding cakes. From time to time a huge air bubble will form underneath the buttercream just like they do with fondant. I know gases are what cause it to occur under fondant but what the heck is causing this under my buttercream?

Same thing - air. After you bc your cake, take a thin blade knife or the tip of your spatula and break the seal between the bc and the cardboard around the bottom of the cake. You'll cover the damage with a border or ribbon.

Easy enough. Thanks!