Virginia - from Fort Smith, AR
It seems like the weight of the top cake layer is forcing the filling between the layers out to the sides. When stacking the cake layers, before you add the filling, pipe a thick line (tip 12) of icing around the outer edge of bottom cake layer, about 1/4 inch from the edge. This creates a dam that holds the filling between the layers. After you add the filling, stack and ice the cake.