I had a violent freeflow the first year I was diving. It occurred in the winter, in about 45 degree water. I had just finished an air-sharing drill with my buddy (double demand on the first stage) and my backup reg freeflowed. It was sudden and violent, and with the backup reg bungied under my chin, my head was engulfed in bubbles, I couldn't see, and the noise was horrendous.
We dealt with it by having my instructor (who was in the water with me and my buddy on a fun dive) donate his long hose. My buddy offered to turn off my tank, but the instructor waved him off. In retrospect, I think that was a mistake, because the whole situation would have been calmer and easier to manage had those darned noisy bubbles gone away.
There was no problem with the inflators, nor would I expect there to be; once the excess IP from the frozen first stage has begun to vent through the second stage, there is no reason for the pressure to blow out anywhere else.
I would suggest, in preparation, to be VERY comfortable with air sharing and air sharing ascents. I also think it is rare for single tank divers to make sure they can reach their own tank valves and turn them -- and if you allow your buddy to turn off your tank, you need to be sure you can reach that valve, if you lose control of your ascent and lose that borrowed regulator.