Link to the quest: https://www.wowhead.com/wotlk/it/que...0/who-are-they

After accepting the quest, the character get a disguise effect, but this doesn't happen. I deleted the cache folder, I've tried to quit the mission, to talk to the NPC again, but nothing happens.

During these tests I was without a ground/flyingmount, the bags were empty and there were no magical effects, or buffs/debuffs on the character.
The weird thing is that other player get the disguise after they accept the quest.