Okay, if you want to accept on authority what occurs when you microwave peanut butter, here's what happened.
I was hoping to make a peanut butter topping for my ice cream. I thought that if I mixed three tablespoons of peanut butter (organic) with an ounce of maple syrup (artificial, sugar-free) in a bowl and microwaved it for 30 seconds, I might get a hot, liquid-y topping.
Instead, the peanut butter mixture simply expanded slightly, like a marshmallow puffing up over a campfire. It did not liquefy at all; in fact the consistency was slightly stiffer than the pre-microwaved peanut butter. So I ended up putting chunks of hot, puffy peanut butter on my ice cream.
Please feel free to experiment by using different styles of peanut butter, either adulterated or not with other ingredients.