there are a number of reasons. sometimes it's the humidity in the air, or the cupcakes are sitting too close to each other when cooling. some people say to cool them totally in the pan; some say to take them out immediately. you just have to play around and do what works for you.
this is what I've done to combat the problem. I only use Reynolds white liners, and I fill them so that they rise a little bit over the edge of the liner. I bake at 325 instead of 350. I take them right out of the pans and make sure they're not touching when cooling. After they're cool but before they're decorated, I put them in a cake box and close the lid, but not all the way. I read on here somewhere that putting them in an airtight container can lead to the liners separating from the cupcake.
I think that's about it. Good luck to you!
My experience with that problem has been too much fat in the recipe. I have a couple cupcake recipes that call for cream cheese in the batter and those always pull apart regardless of how or how long they cool. It's very frustrating because the cupcakes taste amazing...they just look sick. 
I have never had one pull away from a Reynolds liner. I am considering using these exclusively in my business, especially now that they come in different colors and patterns. I only bake extra moist, full fat cupcakes and this is my only insurance policy. I did get some brown foil ones from etsy and so far, so good, but not enough experimenting yet. Reynolds are more expensive, but I never have to redo, and to me, it is worth it.
Quote by @%username% on %date%
%body%