I have personally witnessed three of these, always on a hot day after firing numerous rounds. (I coach speed shooting with teenagers).
A picture. Note the bolt face "coined" into the base of the case and two firing pin hits. This was absolutely not a misfired round that got reinserted. All misfired or misfed rounds go into my left pocket during events and never come out during shooting. The young lady was in the middle of a string for time, I was timing her. The gun sounded louder, I saw a flash of flame, and then I got hit in the neck with the empty case.
We had two more identical events (except my buddy Kevin got "shot" in the neck with the second one and no one got shot with the third.) Shooting timed strings with rimfires requires the timer to have his hand, holding the timer, out near the muzzle. Otherwise the microphone misses the sound of some shots. Your hand is NEVER down range, but this position puts your neck right by the ejection port.
About shade tree gunsmithing and dirty guns - our team had an armorer who is a professional. They were unmodified. He cleaned the guns between kids (ten kids shared three guns). It was a hot day and the guns got hot and stayed hot, despite frequent cleaning (the guns were not torn down between every shooter but were sprayed and scrubbed). If any gun jammed it was torn down. All guns had probably seen a few hundred rounds that day. This is the nature of kids shooting sports, the guns see a lot of rounds. Matches tend to be in the south, in the summer.
I sent pictures and a detailed description to S&W. I never heard back (never expected to hear back). I'm an engineer in the safety business. "Public utterances" come back to bite the company. Until the moment they are ready to go public with a recall it is better to say nothing. Apparently they are not there yet.
All involved guns were sent back to Smith and Wesson, one had blown out the extractor, the others were functional. All came back clean and shiny and this never happened again.