I have tested your case on both Python driver and CCI.
Actually the table db_user you use to test is special, we can see the schema information below:
name CHARACTER VARYING(1073741823)
direct_groups SET OF db_user
groups SET OF db_user
triggers SEQUENCE OF object
There are two SET columns and one SEQUENCE column. These types are special operated in Python driver when we need to fetch them. However, there are some problems because the CCI have not processed successfully.
The problems happen in the test case are:
If we don't use cci_set_free(), it will work well, otherwise, it will be aborted.
But according to the cci_set_free()'s document, we should use this function after cci_get_data have gotten the T_CCI_SET data.