go-ora: TTC error: received code 28 during response reading after "alter session set container=pdb1"

I can’t exec ALTER SESSION SET CONTAINER=PDB1, which results in TTC error: received code 28 during response reading

func doSql( dbh *sql.dbh,sql string) (error) {
   _,err:=dbh.Exec(sql)
  return err
}

In the same connection ALTER SESSION SET NLS_DATE_FORMAT='YYY-MM-DD HH24:MI:SS' executed without problems

Database behind is a RAC CDB, if this matters. Connected User is a C## common User with the needed privileges

testet with go-ora 2.7.9 and latest 2.7.11