The following KB provides information/solution for a behavior that is seen OOB when assigning a user to the 'Caller' field on the incident form. By default, the caller field is a reference field that includes a simple reference qualifier and a dependent field on another field called 'Company.' When an incident is created the company field on the incident record defaults to the company value which is reflected in the callers user record. If a users/admin attempts to change the caller to another user which happens to not be part of the same company that is reflected in the incident record this will not be possible. The behavior observed is that the user which is being searched for on caller will never show up in the reference lookup query.

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This is expected behavior as there is a dependent field on the caller field which has a direct relationship to the company field. Only users that are part of the company which is reflected in the incident can be assigned to be caller field.

There are two possible solutions

1. An admin can remove the dependent field from the dictionary entry of the caller field which would then allow any user to be assigned to the caller field.
2. An admin/developer can configure the incident form to include the company field and then update the company field before trying to update the caller field.