If equipping a character with two weapons using the Dual Wield ability, then attacking another unit with enough force to make only the first strike kill it, the second strike will also attack and the KO label will be displayed twice (once for each hit). This can also be done by using the Doubleshot ability learned from the viera's Sniper class, or the Pummel ability learned from the bangaa's Master Monk class, as well as Doublecast from viera Red Mages and Magic Frenzy From hume Seer.
This can be increased to displaying the KO label up to four times by doing it using the Opportunity Command "Flurry!" with the Dual Wielding character.
This bug has no negative effects on the game itself, and is purely a visual glitch.