I have never heard of that happening. I have heard a Par 36 could set pine straw on fire. But I don't know how you can overload a transformer that is hanging on a wall and set the pine straw on fire. Most transformers have breakers or fuses at least every one I have put in. And they are always plugged into a gfi. I guess if you did not wire not the connections they could spark. They really need to be worried about the homeowners installing lighting more than contractors.