Perhaps a better rule would be that no one can post anonymously at RC.com, in any forum where actual climbing knowledge is required. This would help prevent people from posting utter nonsense like your post above. Randy Vogel thinks back-clipping is a non-issue and so do I. Jay Tanzman, although on the other side of the issue, has also never seen or heard of anyone coming unclipped from a rope in his 20+ years of climbing from a back-clipped carabiner. Together, we have over 75 years of frequent and regular climbing experience. I call BS on you claiming to have seen this twice yourself. Go back to posting in Community where at least your false and misleading posts are harmless.

You can call BS all you like, that doesn't alter the fact that I have seen it happen: once in february last year at Stob Coire nan Lochan, and once in (I think) September the year before at a sport crag called Benny Beg.

Nobody here seems to be debating that the possibility of back clipping at least exists, so why is it inconceivable that it could actually happen?

In addition, consider this: you've clearly been climbing far longer than I have, so doesn't it make sense that you would be climbing with more experienced partners than most, who are therefore less likely to back clip?

Perhaps I misread your previous post. Are you saying that you have merely seen a back-clipped carabiner twice before--or that you have actually seen a rope come unclipped from a carabiner that was back-clipped? Obviously, there is a huge difference. I certainly don't doubt the former at all.

Also, with standard length runners that are often used in trad climbing, it is often not even possible to tell if a carabiner is back-clipped or not. I think someone else mentioned this as well.