It happens to my husband and I all the time, both as Imps and Reps. There are a couple quest instances it always happens (as mentioned above "The Trials" and "industrial Collapse"). Generally we don't do a lot of Heroics, just class and planet story arcs. I am less concerned with the lack of immersion when compared to the extra time to run these things twice. It has started to annoy us badly and we are considering dropping our subscriptions. It is absolutely ridiculous that a major grouping bug in a MULTIPLAYER game isn't being addressed. On some occasions, if both of us back up before the trigger area then the person (who didn't get the update) goes forward alone and gets their update. It doesn't work for all the instances but it does for some.