i would suggest that there are 2 factors- speed and sharpness of the trimmer. Using a diamond credid card sharpener made a huge difference on mine.
the tool is rubbing on the end of the blank causing friction- the higher the speed the more generated in a given time and ultimately burning. If it is blunt instead of cutting, it is causing more friction, same result.
You will get the same if you use a sander and a fine grit paper.