I have had the same experience. Each time I go to a war zone for this mission, I end up in the 'borg being repaired' scenario with other people. We accomplish the mission, but no one gets credit for it.
One time I was in the scenario where it was 'do it before the Klingons do', but I didn't get credit for that either when we won.
I haven't tried it in the last two weeks, so perhaps it will be fixed.
Read some recent posts... it is fixed, within the last 2 weeks...:p
You need to go back and talk to Mazka before you get credit for the mission. It doesn't just give you the reward after the mission is complete like most other assignments (which is whack if you ask me).