On Thread #971482 a changed behaviour it is posted.

Now i remember it.
It is a VFP8 bug fixed.

Cause:
with SET ANSI OFF,
any string function that can set the string expression to ''
it is a candidate to show a VFP bug.

The because of a bug in the code that uses the indices.

VFP must bring back the same ones turns out to you with:

...  WHERE CExp1 = CExp2
...  WHERE CExp2 = CExp1

is that it uses an index, is that it does not use it.

VFP standard code, have a limit, and it optimize the left expression only,
then if a zero lenght string key exists on the index,
the two queries return a different set.

Sin that, instead correcting the error in the search code,
the team fix the error disabling the optimization when
in the expression is present a function that can generate one zero lenght espression ''.

Then:
into VFP8

STRTRAN()
CHRTRAN()
REPLICATE()
STUFF()
STUFFC()
TRANSFORM()

they are not optimizable

into VFP9, the Team have has added these to the not optimizable functons list
for SET ANSI OFF:

ALLTRIM()
LTRIM()
TRIM()
RTRIM()
LEFT()
LEFTC()
RIGHT()
RIGHTC()
STRCONV()

they are not optimizable.

But the VFPT job it is not completed !

The same bug it is live on this code ( i test this into VFP9 Beta):

CREATE CURSOR CONTDB (LN C(10),lencode I )
INSERT INTO CONTDB VALUES ('',1)
INSERT INTO CONTDB VALUES ('',0)  && THIS IS EQUAL TO LEFT(,0)
INSERT INTO CONTDB VALUES ('VOSS',3)
INSERT INTO CONTDB VALUES ('VOSS1',2)
INDEX ON SUBSTR(ln,1,lencode) TAG TT

CLEAR
SET ANSI OFF
=SYS(3054,11)
SELECT * FROM CONTDB WHERE 'V' =  SUBSTR(ln,1,lencode)
SELECT * FROM CONTDB WHERE   SUBSTR(ln,1,lencode) = 'V'

Of course the same bug appear with:

SUBSTRC()
PADR()
PADL()
PADC()
GETWORDNUM()
SPACE()

For fix the bug, VFPT have cut the optimization;
but this is a simple shortcut mode only for workaround the seek bug;
if VFPT rewrite the C seek inner code,
VFP can optimize these expression
on the SET EXACT OFF context.

Fabio