That is correct, and I suspect it might be a bug that has been fixed in more recent versions because I cannot reproduce on my 19c version
SQL> create table test (
2 tst_id number generated by default as identity,
3 tst varchar2(255)
4 );
Table created.
SQL>
SQL> create flashback archive flashback_test
2 tablespace demo
3 retention 1 year;
Flashback archive created.
SQL>
SQL> alter table test flashback archive flashback_test;
Table altered.
SQL>
SQL> insert into test(tst) values('Test1');
1 row created.
SQL> commit;
Commit complete.
SQL> host sleep 120
SQL>
SQL> update test set tst = 'Test2' where tst_id = 1;
1 row updated.
SQL> commit;
Commit complete.
SQL> host sleep 120
SQL>
SQL> update test set tst = 'Test3' where tst_id = 1;
1 row updated.
SQL> commit;
Commit complete.
SQL>
SQL> select tst, versions_starttime, versions_endtime
2 from test
3 versions between scn minvalue and maxvalue
4 where tst_id = 1;
TST
----------------------------------------------------------------------------------------------------------------------------------
VERSIONS_STARTTIME
---------------------------------------------------------------------------
VERSIONS_ENDTIME
---------------------------------------------------------------------------
Test1
27-SEP-21 06.25.58.000000000 PM
27-SEP-21 06.28.09.000000000 PM
Test3
27-SEP-21 06.30.20.000000000 PM
Test2
27-SEP-21 06.28.09.000000000 PM
27-SEP-21 06.30.20.000000000 PM
SQL> host sleep 120
SQL> select tst, versions_starttime, versions_endtime
2 from test
3 versions between scn minvalue and maxvalue
4 where tst_id = 1;
TST
----------------------------------------------------------------------------------------------------------------------------------
VERSIONS_STARTTIME
---------------------------------------------------------------------------
VERSIONS_ENDTIME
---------------------------------------------------------------------------
Test1
27-SEP-21 06.25.58.000000000 PM
27-SEP-21 06.28.09.000000000 PM
Test3
27-SEP-21 06.30.20.000000000 PM
Test2
27-SEP-21 06.28.09.000000000 PM
27-SEP-21 06.30.20.000000000 PM
SQL> host sleep 120
SQL> select tst, versions_starttime, versions_endtime
2 from test
3 versions between scn minvalue and maxvalue
4 where tst_id = 1;
TST
----------------------------------------------------------------------------------------------------------------------------------
VERSIONS_STARTTIME
---------------------------------------------------------------------------
VERSIONS_ENDTIME
---------------------------------------------------------------------------
Test1
27-SEP-21 06.25.58.000000000 PM
27-SEP-21 06.28.09.000000000 PM
Test3
27-SEP-21 06.30.20.000000000 PM
Test2
27-SEP-21 06.28.09.000000000 PM
27-SEP-21 06.30.20.000000000 PM
I suggest you raise an SR for this one