For some reason, no matter what I'm fighting in my current save, kwon and lucia leaves my party claiming I've hurt innocent people.
This happens when I was attacked by the robots at the old monster army base (which are hostile). I re-loaded a save just before the battle and went back to the Bizarre. I've tried completing "A Very Hostile Takeover" quest from Charley and Flab, the same thing happens.

Is that a known bug?

Unless you're actually accidentally hitting friendlies with area-of-effect attacks (which can make them turn on you instantly - this happens with any friendly, except animals) - then you have most likely found a bug. Not sure how common this is, I haven't had it happen to me yet and I'm near the end I think.

I suspect you may have hit one or two innocents in a previous fight when you made that save, and for some reason that value has carried over and triggers when you start the next fight?

My only suggestion would be to restore from an earlier save and see if that fixes it?

Had the same problem during an attack on raanger HQ I reloaded the save a few times and turned out if i destroyed one of the base turrets they would leave the group. It must have been the one with the broken timing belt ;)