I've been baking professionally for over 12 years....this still happens to me periodically. I think it's definitely a heat thing: taking the cupcakes out before they're quite done, in the cheaper "home" version of cupcake pans, cooling too quickly tends to pull away more. Definitely a thinner paper liner is better bet. We too, use the thin tulip liner and since switching to them have not had a problem. Time to invest in some professional grade pans for home. They are expensive but worth it. And remember, if you find cute little liners that you simply must use but you know the cake will pull away, you can always use the thinner simple liner to bake in, then after they've cooled completely, pop them into the cute liner using a tiny drop of either royal icing, or a drop of Elmer's glue. I know how frustrating this is....good luck.