Interbase SQL multiple left joins: not working?!

I have used ISQL to create an interbase database structure with three
tables:

table1 LIST:             contains four fields that point to table2 (this field
can be NULL)
table2 AUTHOR:          contains one field that points to table3
table3 PERSONEL:        contains field "NAME"

Now I want to create a select that contains the fields of table1
together with the "name" fields of table3. This takes 4 left joins
with table2 and 4 left joins with table3. Using ISQL, the results are
incorrect.

When using MS Access (same table structure) the SQL statement returns
the correct answer.

I'm using Delphi 1.0

Does anyone know what causes the problem? It seems to me that
Interbase Interactive SQL Version WS-V4.0C is not working correctly.

Thanks in advance,

Lucas

P.S.: For whom is interested...

SELECT DISTINCT PERSONEL.NAME, PERSONEL_1.NAME, PERSONEL_2.NAME,
PERSONEL_3.NAME,LIST.OMSCHRIJVING
FROM (((((((LIST
LEFT JOIN AUTHOR ON LIST.FIRST_ID = AUTHOR.ID)
LEFT JOIN AUTHOR  AUTHOR_1 ON LIST.SECOND_ID = AUTHOR_1.ID)
LEFT JOIN AUTHOR  AUTHOR_2 ON LIST.THIRD_ID = AUTHOR_2.ID)
LEFT JOIN AUTHOR  AUTHOR_3 ON LIST.FOURTH_ID = AUTHOR_3.ID)
LEFT JOIN PERSONEL ON AUTHOR.PERSON_ID = PERSONEL.ID)
LEFT JOIN PERSONEL  PERSONEL_1 ON AUTHOR_1.PERSON_ID = PERSONEL_1.ID)
LEFT JOIN PERSONEL  PERSONEL_2 ON AUTHOR_2.PERSON_ID = PERSONEL_2.ID)
LEFT JOIN PERSONEL  PERSONEL_3 ON AUTHOR_3.PERSON_ID = PERSONEL_3.ID;