I share your pain as the only time this happened to me was when I was main-tanking as well. As you say, it only really interferes in that you can't really dodge Slipstream. You should have solid hate at that point and the Follow-The-Leader portion doesn't require you to target her, so not horrifically problematic. She re-appeared when she summoned her second set of sisters. However, the cause is still unknown to me.