Wondering Why my Sourdough Ruined My Cast Iron?

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I was wondering if anyone can tell me what caused the finish on my cast iron dutch oven to come off?  I recently started baking sourdough bread in it and after baking two loaves of sourdough managed to completely destroy the finish.  I love this pan, (and all cast iron) and have been taking really good care of it for years so am very upset to have ruined the finish on it and don't know what I did wrong.

When baking the sourdough I heated the dutch oven in a 500 degrees oven for an hour, then added the dough with a quick mist of water, and put the lid on it to bake. 

The bread turned out great, but huge flakes of seasoning came off my dutch oven.  I thought this may be from overspray when I misted the dough so after oiling and baking the pan to try and restore it, I tried to bake bread in it again the next day but misted the dough outside of the pan before adding it to the hot pan.  This time even more of the seasoning cracked and peeled off.

Does anyone have any ideas why this happened?  I know many people bake bread in their cast iron dutch ovens and don't know what I did to cause this.

Thank you!

It is a 6 quart Lodge Cast Iron.  I have used it for years and always dry it well and oil it after I use it so it had a nice seasoning finish on it until this week that is.

Lodge brags about their natural patina.  I'm wondering if you got a fake Lodge as that looks like some kind of fake coating coming off.  I can't imagine a natural cast iron coming apart at baking temps.

No, I ordered all my cookware directly from the Lodge website.  I even asked them if they knew why it came off but they just said it could have been a variety of reasons.  I was hoping for a more definitive answer.

Seasoning is just a layer of polymerized oil. Build up a thick enough layer and subject the cast iron to high enough heat and the seasoning WILL flake off. This is why vintage cast iron is so prized; you can find the most built-up, crustiest old skillet at a flea market, toss it in a little backyard fire and cook all the old seasoning off. Then you can start from scratch, building up a nice new layer. 

Long story short, heavy layer of seasoning+high dry heat=flaking.