Saw it again today, and I can kinda figure out why it's happening.
This time, it was after P+K. I noticed that every time I buffer in the Super Launcher, I slide from the A button (Throw) to the X button (Block). It's an old habit I picked up when I first started playing DOA and would buffer in throws too quickly, so I'd hold the guard button to either guard or charge the throw if I timed it right.
Alright, so what's happening (I think) is that during the +26 stun of P+K, I buffer in the 41236T and slide to the guard button right as Bass is at neutral, so the game starts the animation for the Super Launcher but then changes it's mind and has Bass block. He even throws his arms up in the air and yells "FI!-" and then starts blocking.
I made it happen again right after but can't get it down since. I'll start practicing it, as I think you could tease out reactionary low holds against some opponents with it. And that would be pretty sweet.