What the muffin?

I have been making THESE banana bread chocolate chip muffins since I can remember.  It's the first recipe I remember learning from my mom, and since then I make them all the time.  I have always used margarine when making these muffins, because that's what I used when I learned the recipe, so that is what I always use.  I have made these muffins literally hundreds of times, I know the recipe by heart, and they have never EVER gone wrong...until yesterday.  The only thing I changed?  Butter instead of Margarine.

I'm still not sure what happened.  I have seen a lot of things on Pinterest lately about butter being way better than margarine, so I have been buying butter sticks rather than margarine sticks.  I didn't think it would matter, until I pulled the muffins out of the oven and they looked a little different.  Usually they pop right out of the muffin tins with ease and look fluffy and beautiful like this:

Instead, they were sunken in and stuck in the muffin tin (and yes, I greased the pan beforehand).  When I finally pried them out, they looked like this:

Epic Fail.  I was shocked, because I have never not had my muffins turn out.  I then did what most girls do when things go wrong, and texted my mom for advice. She just happened to be with a few of her friends, and she told me they all agreed that margarine is best for baking, and butter is best for cooking.  So, in the future, I won't believe everything Pinterest says, and I will stick to what I know and what works best.