While I was doing my first run (Without a Recording) this happened.
For this run I wasn't recording until I got up to this point, so I wasn't able to show how to actually do this odd glitch.

this is known, but i'm not sure if anybody knows why it happens

We know how to replicate this bug already: Have Susie downed by an attack, then on the turn she gets up, dont press anything until speech boxes go away. It's that simple so it has occurred to many people who have played this game.