I've seen this happen when you've got healers spamming medica as the red-tether runs in. Shield Lob/Tomahawk + Flash and just start comboing the shit out of it. Save Provoke for a few seconds or the AoE heal/regen will instantly overcome the provoke.

I find this to be a bigger issue with DF groups than FC runs. When I first ran it with my FC, no issues at all with healers nabbing hate on add. When I OT'd for a random shout group.... WHM was goin nuts with hate on the adds.