Sometimes important user information is stored in user's 'data' field in serialized form. When comment is loaded only certain user fields like 'name', 'signature', 'signature_format', 'picture' are fetched. Drupal allows to fetch additional user data at any time of course, but that would require an extra SQL query - something that should be always evaded, if there is a better way.
I propose to fetch user data field as well.
The patch is rolled against 7.19.