Why does microwave popcorn burn? I've been experimenting some with do it yourself microwave popcorn, and some trouble getting the 'burn time' right has led me to a question that I can't find a good, definitive answer to.

What is the scientific explanation for the mechanism for how popcorn burns?  I'm not looking for "Because it gets too hot", but what gets too hot, how does it actually get that way?  Microwaves don't just heat everything up (like a stove does), so it's not as straightforward as that.  You can put many foods inside of a microwave and massively overcook them without burning.  So what's special about popcorn that causes it to burn?  I would prefer either a detailed chemistry/physics answer, or  a reliable, science-based source.  From looking around online, there are lots of semi-reliable opinions on this, none of which agree with each other.

For example, this very old Chicago Tribune article on Popcorn seems to say that it's a problem of "finding" the kernels.  Really?  Others claim it is the kernel overheating, or the bag overheating, or the oil overheating (yet no-oil still burns, though that may contain some oil from the corn itself I suppose), or gnomes lighting them on fire with matches (Well, no, but it's about as reliable as anything else I've found).

And related to this, what control do I have over this other than time.  On a stove, I can reduce the heat; for example, if I'm cooking on the stove with butter, if I cook at '3' I can cook almost all day without burning my butter, while at '4' it browns pretty quickly; so I can choose whichever setting based on that.  What in a microwave would be similar (in allowing me to cook the kernels more thoroughly - not just take longer - without risking burning).  What ingredients or microwave settings can I control?
I think most of your confusion comes from the paradigm of water.  Water (under kitchen conditions) will not get any hotter than its boiling point.

Oil has no such limitation.  You microwave will heat oil well past water's boiling point and all the way up past the smoke point to the flash point of the oil.  At the flash point, the oil will actually catch fire.

If you put a bag of popcorn in a microwave on high for an extended period of time you'll see this as actually burned corn.

Also, if a significant mass resting against the paper bag gets above paper's flash point (451 degrees F) it will also catch fire.

My little sister has proven this true time after time.