100% still an issue. This happens when the target LOS and you turn rapidly. Happens with more than just DB.

This bug is related to all ultimates. In short the ultimate cost is consumed before the ultimate takes effect. Had a case yesterday when using the necro colossus ulti and a npc walked through me and then the animation canceled but still lost my ultimate (yes, I was trying to be a bad person. Just the personality of my toon)

Would not be surprised if this is also linked to the time when I did Falkreath Hold and had a double KO with the boss. (was killed by the shout mechanic around the same time as dots killed it, counted as a clear so yay)

So... Perhaps a server based issue where the ultimate cost is taken based on one process queue and the animation and effects is in another queue, and then these 2 queues are not in sync and it is possible that when the one event validates everything is fine, but the next runs 2ms later and then gets a error message because your status changed in that 2ms on the server side. The 2ms is a total guess, in theory as long as the it is 2 distinct queues which checks separately the problem can happen even if it doesn't sync up to clock cycle on the server.