In certain circumstances, the shock to the grinder may be great enough that the motor doesn't have time to stall, but rather the ring burr carrier can act as a mechanical "fuse" . This is the second safety system. This shows up as inconsistent grind and a broken tab on the burr holder. In the past, our main drive gear was the weak link and this was inconvenient to our users, because this was not a user-replaceable part. We have since redesigned our entire gearbox so it never fails. As a result, 100% of the torque produced by the grinder is resisted by the ring burr carrier. The ring burr carrier can easily be replaced by the end user, so the grinder is back in action quickly. We have over 180,000 units in circulation and we go through a little less than 3000 burr holders per year. This works out to 1.7% of our Encore, Virtuoso, and Preciso grinder owners replacing ONE burr holder per year (98.3% do not). In almost all cases, failure of this part is due to foreign objects (stones, screws, etc) or unroasted coffee beans getting into the grinder.
Now you know why we have a plastic burr holder and why it's a good thing!