I have an absolute tank of a character.   "Nikki" took the Demon King down to zero HP.   Nikki's masterwork gladius has "icy", "sharp", etc

So the Demon King is in Supine stance, with 0/160 HP, although she still has 25 Stamina.

But the fight isn't ending.  Each round the Demon King does nothing, and Nikki clobbers her.  The Demon King's statuses include Sleep, Injured (3), Frostbite (24), Chill (34), Bleeding (55), Dazed (7).

What's going on?  A bug?  Do I need to sit back and let the DK wake up to realize she's defeated?

My guess was correct.  I needed to sit back (Block) for a few rounds to let the DK regain consciousness to use her healing for full HP again.
But with huge bleeds stacked up, she was easy to take down to zero again, this time for good.

Not sure if I'd call this a bug, but it's weird.  One lesson is that the combination of "Icy" and "Sharp" on a weapon is pretty handy against the DK.