Melinda quest bug

[Desath]

Playing a yeek solipsist, I encountered a problem with this quest.

On the last level, I used inner demons on the 4 mobs trying to sacrifice Melinda. I killed the 4 sacrificers with plenty of time left on the counter, but did not receive quest success as the inner demons were still "live". Eventually, the counter ran down to zero, and the demon quest boss appeared.

I anticipate that this is an unintended consequence of the inner demons skill?