Am I missing something? The only time a mob should turn white after killing someone is if no one else in the party is engaged. As far as I am aware, even a white mage standing in the back with a weapon out should keep claim in the event of a death or a charm. As for Charby, I'll assume you're talking about DoT kiting? Again, no weapon drawn = you have surrendered the monster.

I have never ever had something I was actively engaged to go unclaimed. Elaborate, please.