I wonder what's going on with yours, I've used the same technique (torch, heat gun) and have never had a problem. Sounds like you're letting yours burn a lot longer than I do (I go a couple of minutes, tops, burns maybe 1/5 of the first row). It's not unusual, though, for it to get hot enough for the second row to start smoldering, I have to watch that and make sure it's out before I walk away from it.
I'm wondering if there is a moisture problem in the pellets. I know you nuked them, I would think that should have dried them out. I keep mine in a tightly sealed 5 gallon bucket, in a very dry shed, and I've never had any trouble. The pellets that are burning now, are they leftover from yesterday, that could have dried out more through your whole process here?