>you have a repro bug code ?

ja. i modi your code a bit. now, try this code 1 time without the '.dbf' behind all of the table names and one time with it.

OldDefa = set("defa")

CD SYS(2023)
MD dir1
MD dir2

close data all

CREATE TABLE dir1\table1 FREE (F1 I , F2 C(1))
INSERT INTO (ALIAS()) VALUES (1,'a')
INSERT INTO (ALIAS()) VALUES (2,'b')
USE

CREATE TABLE dir2\table1 FREE (F1 I , F2 C(1))
INSERT INTO (ALIAS()) VALUES (1,'A')
INSERT INTO (ALIAS()) VALUES (2,'B')
USE

set defa to (SYS(2023) + "\dir2")

SELECT ;
		tab1.f2 ;
	FROM ;
		(SYS(2023) + "\dir1\table1.dbf") tab1 ;
	WHERE ;
		tab1.F1=1 ;
	UNION all ;
		SELECT ;
				tab2.f2 ;
			FROM ;
				table1.dbf tab2 ;
			WHERE ;
				tab2.F1=1 .and. ;
				tab2.F2 not in (sele f2 from (SYS(2023) + "\dir1\table1.dbf") where F1=1) ;
	into cursor cur_test

sele cur_test
brow last

CLOSE TABLES ALL
set defa to (SYS(2023))
DELETE FILE dir1\table1.DBF
DELETE FILE dir2\table1.DBF
RMDIR dir1
RMDIR dir2
set defa to (OldDefa)