Okay, I deleted those posts as agent_smith was right. It was way off topic. As for everyone demanding proof, I'm sorry that I don't have video of me falling. I'm sure it would be amusing.
Scott, I was not disparaging the knot. I was simply reporting what happened to me and that I thought it presented a possible danger that I had not considered until it happened. Yes, it is probably a fringe case, but most accidents are.
The why:
I have a friend who is worried about knot size and stability on hard slab. He explained that a tie-in that I had discussed with him was large enough to push him off a route that he had been trying (I think in Zion, but don't quote me) and he was looking for something almost as small as a bowline backed up with a double overhand on the returning eye-leg (what he said he switched to when his retraced 8 pushed him off the wall). Scott's lock is one of the smallest knots and was the third I "tested" his scenario on (I was just messing around).
I simply posted my experience. I'm extremely surprised that no one is able to reproduce it when trying to reproduce it, considering that it happened to me when I was just feeling what different knots felt like on slab when my foot slipped. I've never climbed anything where a retraced figure 8 could push me away from the wall or even bother me. That is all that I was doing. I was not attempting to bring any knot to failure.
The how:
https://imgur.com/a/O4ZSFC6This imgur album is as close as I can come to explaining what probably happened to me.
I was tied into the left pictured knot in agent_smith's picture. I can not reproduce it on the middle pictured cowboy bowline version that also grabs the returning eye-leg. I've never tied the cowboy bowline with the lock outside of the eye-legs until just now, to add it to my naming system text document.
The protuberance pictured in agent_smith's photo caught the opposite side of the collar as presented in his failure mode test picture. The snag was limestone and was not nearly as pointy as presented. It was basically the corner of a cube. I may have fallen to the opposite side, allowing a better snag. I don't know, as it took a total of maybe 0.5 seconds and was completely unexpected.
The snag would only pull in slack left by the belayer, though this is often enough to pull the knot out of reach, especially when clipping. The collar was not significantly elongated by the time I landed (a few feet, and no injury).
I had already run my hips into the wall a couple of times and the collar was not as tight as when initially set. Nothing had been done to it, intentionally, other than climbing a slab where my knot hit the wall a couple of times.
The first picture is the knot set as tightly as possible. Even fully set, the simple bouncing of walking 10 feet allows some of the returning eye-leg to feed into the collar and give it the collar hole in the pictures. The knot does not lock down into an immovable locked knot in my rope, though the tail stays put nicely, despite that. The next picture is a little jiggle. I'd guess that tiny hole or simply the width of the rope of the collar is all that could have been snagged. I do not believe the knot would have opened further than the zoomed in picture by the time that I fell.
This is used rope with no core or sheath issues. I do not know the brand or model, but it was originally purchased by a climbing gym before being given to me to practice tying with so I didn't have to pull out 60m or use the small nylon I had laying around.
My theory is that my position and the orientation of the knot to my harness allowed the ongoing eye-leg to receive a small tug before the returning eye-leg was set and added friction to the standing/nipping parts. From how I usually feed my harness loops, this would mean that my leg loops pulled first, as I usually feed my harness bottom to top. Once the standing end, the nipping loop and the ongoing eye-leg overcome the initial friction, there isn't much to stop it from feeding through, at least in this rope.
I do have trouble reproducing this in my stiffer, fuzzier rope.
Anyway, that's all I've got to say on the matter. I just thought that since it happened, I should tell someone.