Yes, that happened on an OTS that I have. Over time, drippings on the ash in the bottom of the bowl built up, and it was hard to tell it had built up so thick when scraping the bowl using the one touch system blades. The blades "seemed" to scrape everything off leaving behind a thin layer of ash on the bottom of the bowl, but the truth is that over time that ash layer was about 1/4" thick. Once it reached about that thickness I got a grease fire from the drippings in the ashes on the bottom of the bowl.
The fire was just as you described and can see in the photo, coming from the bowl, and had a thick black and smelly smoke. I tried to let it burn itself out, but it outlived my charcoal. So I suffocated it and the next day went to checking out what was on the bottom of the bowl.
I used a plastic putty scraper to scrape out the ash build up. I found that over time, my blades had slowly bent upwards and after cleaning they were no longer flush with the bowl. I could have simply removed them and bent them back and re-installed making them fit as I tightened it up, but I decided to just go out and get some new blades, new handles and new grid to look like a new kettle. You don't have to do that of course.
Every so often I hit it with the scraper again, because it will build up liek that if you don't clean out down there. The one touch blades just can't "dig down" into that stuff, and will instead just start sliding over the ash causing the build up.
This could probably be translated into an single sentence comprised of perhaps no more than approximately 15 words or some other such amount, but I do not have a translator yet.