See what the lookup is, look at the lookup what it is it displaying and what it the hidden field.
When the lookup is dynamic and it is querying the cmn_sec_users for the id and last_name + first_name that is what you need.
When it is querying srm_resources and the hidden key is id then you information comes from the srm_resources.
If the hidden key is user_id then it comes again from cmn_sec_users.