Vorici Low life Mission Bug

Here is a link to the picture showing the bug (sorry I cbf figuring out how to resize image to fit the forums).
http://i.imgur.com/pqbNm5x.jpg
The mission was to keep rogue on low life for 10s.
It shows the mission status on the right saying "Mission complete. The target has been dealt with." and also "keep the target alive".
It also shows that the mission is incomplete at the bottom as it says "complete the mission".

What happened was that Xandro Blood drinker was on low life, the countdown begun and he killed me before the countdown finished. I went back and he disappeared and can't complete the mission.