I think that might be a storage problem. I've seen it with spinach pies that have been sealed up too soon after baking, while there was still a lot of moisture to be trapped. I think it can also happen when there's not much butter/oil on the layers of filo-- Olga's (before it went under) used to sell frozen spinach pies in our grocery store, and, at some point, they stopped using butter in the recipe. I learned that I had to apply some butter or oil before I baked the dratted things or they'd be soggy on top.