I originally observed this on a modded game, but was able to replicate it on an unmodded game. I haven't seen this mentioned anywhere else, but if it's a known bug, ignore me. I unfortunately don't have a save, but this has occurred multiple times now, on multiple games.
I've had banters fire at strange times...namely, during the spirit warrior sequence in WK and while the epilogues are rolling. It doesn't usually mess up the game, so I figure it's not an important bug, which is why I didn't mention it right away or keep a save file. But, it's been bothering me lately, so I figured I'd post about it.
I'll just be doing the spirit warrior sequence, fighting the ghost or dog or whatever, and out of nowhere someone will start talking. It's jarring. Once they've finished talking, it usually goes right back to the spirit warrior sequence and continues on. Sometimes, though, it screws up the whole thing, and makes me have to start over, which is frustrating because I hate that sequence.
The other time I've had a banter fire is during the epilogues...I clicked "done" on an epilogue, and the screen jumped back to the throne of bhaal, where a banter fired. That was pretty shocking. Once the banter was over, it went right bak to the epilogues. Not a big deal, but still pretty weird.