I know that KP isn't guaranteed after a mid kick hold which sucks. I found that out awhile ago which kinda irritated me since since after doing that you can net some serious damage compared to just doing 6PK after the hold. And as you saw, I tried to remake that same scenario w/o the CPU acting on it's own.
this has actually happened to me a couple of times, not with momiji though. at the time i wondered if naos' kick string had high crush, but honestly i wouldn't call it a glitch, just...bullshit that works sometimes
I don't know if this is an AI thing, a stage thing, or if it's an issue with Momiji's KP string when you hit a back turned opponent. Tried to repeat it, but it didn't work.