As title says, Worgen players cannot pick up angelic feathers (Priest talented run speed boost) while darkflight is active. In the past this has made sense as darkflight and feathers were both 40% run speed boosts and did not stack.
However, there are two issues now:
1: It is now possible for feathers to be talented up to 50% run speed boost (as oracle). This now means the feather should be a stronger run speed boost than darkflight, but worgen cannot access it while darkflight is active.
2: Next patch darkflight will stack with other run speed increases. Not a current concern but this should be fixed prior to that patch.