Here's what happened:
I entered Ravel's Maze and hit F5 for some quicksave action. Then I decided that I needed to rest. After that, I head right and encounter the Trigits. Each time I knock one down, another comes up where it spawned.
I was having trouble replicating it, until I remembered that a banter came up at the EXACT time I killed the first Trigit (the xp notice even showed up in the dialogue window instead of on-screen). Likely an uncommon problem, in that case. Still it might be worth considering preventing banter initiation during combat, for robustness.
