Some help needed

If i put Form DataEnvironment Cursor Buffer Mode Override = 5 Optimistic
Table Buffering
the following code work very strange. In some cases it replaces filed
values with some corrupted string on
even does not replacing anything

Setting
Form DataEnvironment Cursor Buffer Mode Override = 5 Optimistic Row
Buffering
everything works fine

LOCAL oldkood, ckomp,lSuccess2, lSuccess1
oldkood="21"
ckomp="2"
 BEGIN TRANSACTION
         UPDATE Kliit!Oppeplan SET Oppeplan.kavakood=ckomp ;
           WHERE Oppeplan.kavakood==oldkood
     BEGIN TRANSACTION
           UPDATE Kliit!Kavayks SET kavakood=ckomp ;
             WHERE kavakood==oldkood
             lSuccess2=TABLEUPDATE(.T.,.T.,"Kavayks")
             IF lSuccess2
               lSuccess1=TABLEUPDATE(.T.,.T.,"Oppeplan")
               IF lSuccess1
                   END TRANSACTION
                   END TRANSACTION
               ELSE
                 ROLLBACK
                 ROLLBACK
               ENDIF
             ELSE
               ROLLBACK
             ENDIF

Kuido