I was fighting against some bots on Arcade as a one man Big Band against a threesome team, and when I pulled off Big Band's n.MP attack as I was fighting Valentine and she flew over me, she landed behind me and just did nothing as long as I held Big Band in his n.MP attack state. I figured for at least a few seconds that this was normal AI delay between attacks (I was fighting on Normal difficulty) but all Valentine did was crouch, stand up and repeat. However, it did stop after I left the n.MP pose, and it hasn't happened to me since, so I couldn't be sure if this was a legitimate bug or a one-off bug.
