Dying immediately after killing Rootdredge marks him as permanently uncompleted

Was attacking the boss Rootdredge, killed him and 0.1 seconds later died to an exploding minion. When I checked my map, he was marked as incomplete (his icon is still opaque and using the "undefeated" icon text [...the trees move, you best move as well...).

The problem is, even after killing him again in a completely new instance, he is still marked as incomplete. Rendering him impossible to "complete" for my character.

I think that this may be happening to everyone at the moment (he shows as incomplete for one of my recent characters that killed him).