The latest update does

```
class ExternalUsergroupsController < ApplicationController
  before_filter :find_by_id, :only => [:refresh]

  def refresh
    @external_usergroup.usergroup.refresh_ldap(@external_usergroup)
    redirect_to :usergroups
  end

  private
  def find_by_id
    @external_usergroup = ExternalUsergroup.find(params[:id])
  end
end
```

but in generic case there is no (and there will be no) refresh_ldap there.