Markdown now support users from groups

app/models/project.rb

@@ -68,6 +68,7 @@ class Project < ActiveRecord::Base
   has_many :deploy_keys, through: :deploy_keys_projects
   delegate :name, to: :owner, allow_nil: true, prefix: true
+  delegate :members, to: :team, prefix: true
   # Validations
   validates :creator, presence: true

lib/gitlab/markdown.rb

@@ -166,7 +166,7 @@ module Gitlab
     end
     def reference_user(identifier)
-      if member = @project.users_projects.joins(:user).where(users: { username: identifier }).first
+      if member = @project.team_members.find { |user| user.username == identifier }
         link_to("@#{identifier}", user_path(identifier), html_options.merge(class: "gfm gfm-team_member #{html_options[:class]}")) if member
       end
     end