Is it normal that I keep burning my seasoning off my cast iron? I use cast iron, a lot.  But I've got a problem, whenever I do something that requires high heat or really anything over medium (which is somewhere around 450-500F on my stove according to my IR thermometer), the seasoning burns off my pan!  There's smoke and all that and then by the end of the cooking, large parts (mostly in the middle outward where its hottest) of the pan don't have any seasoning left and I can see the bare cast iron. Above 600-700F, I definitely expect it but it happens just above/around 500F for me.

Am I doing something wrong?  Is this normal?  Is there a way to season the pan that keeps this from happening?  I've just been using canola oil.
No, this isn't normal. A little flaking, perhaps, when you go over 600°F, but 500°F shouldn't do anything. It shouldn't even smoke.

Something is wrong with the seasoning on your pan. From the fact that its smoking, I'd guess its not sufficiently baked on. Alternatively, maybe the pan wasn't clean when you applied it.

If its just not baked on, I'd remove all the flaking bits (with some harsh scrubbing, sand paper even), clean it thoroughly, then bring it to around 300°F (stovetop or oven). This will make sure it is completely dry. Spread a thin layer of high-iodine value oil (flax seed is great, soy is pretty good and cheap and easy to find: look for the bottle that just says vegetable oil and check the ingredients, it's probably soy). Spreading is easy with a paper towel.

Next, toss into a very hot oven, 400–500, smoking is expected. Bake for 90 minutes, then turn the oven off. Allow pan to cool with oven. Once its cool, touch it. If its at all tacky, put it back in the oven, and bake for another hour (once again, allowing to cool with oven). It should be a shiny black at this point, and not at all tacky.

You can repeat the process to add more layers. Two should be reasonably non-stick to start cooking on. 

If it still peels off after this, you're probably going to need to strip the seasoning and re-season the pan, after stripping it to bare metal. See What&#39;s the best way to season a cast iron skillet? to season it from bare metal.