Aggregate function with Join stop working under certain condition

I am joining 4 tables (doc, bpt, con, emp) - emp and doc relationship is
one to many. I want to only one doc record per emp as condition shown
below:

The query below successfully returns desired result (returns 4 records):

Select bpt_key, emp_full_name, con_full_name, max(doc_date_created) as
doc_date_created

from bpt

LEFT OUTER JOIN doc ON bpt_emp_key = doc_emp_key

INNER JOIN emp on bpt_emp_key = emp_key

LEFT OUTER JOIN con ON emp_con_key = con_key

WHERE bpt_com_key = 22 and bpt_status<>-1

GROUP BY bpt_key, emp_full_name, con_full_name

However, I wan to add one more doc column but as soon as I add one, it
try to return all unique doc records. Could you tell me what am I doing
wrong here please?

As soon as I add one more column, it returns 6 records:

Select bpt_key, emp_full_name, con_full_name, max(doc_date_created) as
doc_date_created, doc_subject

from bpt

LEFT OUTER JOIN doc ON bpt_emp_key = doc_emp_key

INNER JOIN emp on bpt_emp_key = emp_key

LEFT OUTER JOIN con ON emp_con_key = con_key

WHERE bpt_com_key = 22 and bpt_status<>-1

GROUP BY bpt_key, emp_full_name, con_full_name, doc_subject

Kindest Regard,

Naoko