Vorici mission to kill guards fails with odd message while rogue exile is alive

Vorici gave me a daily mission, I believe it was "kill the guards". I was having the rogue exile chase me away from his minions, when the mission apparently failed. The rogue exile was still alive. I thought I had missed a timer, or something. However, I think it was a bug, because Vorici's quest tracker text just said "lvl:" after this happened. See screenshot.



I typed /bug in chat after this happened: reference 2,460,947,137. I was playing my level 84 witch Wenin, in Standard league, on client 1.2.4e.

One possible trigger condition: I was leading the rogue exile back into the room where Vorici was waiting. I might have clicked on Vorici, but I don't think so. I think we were both just close to Vorici, but perhaps that is the odd condition that triggered it.

To be honest, I wasn't paying that close of attention before it happened, so I may be remembering some detail wrong. However, the corrupted quest tracker text afterward makes me think it really was a bug, and not purely my imagination.