I have used following test code:
report ztest.
TABLES sflight.
DATA: gt_lfa1 TYPE TABLE OF sflight,
lw_lfa1 TYPE sflight.
SELECTION-SCREEN: BEGIN OF BLOCK b1 WITH FRAME TITLE text-001.
SELECT-OPTIONS: so_konzs FOR sflight-SEATSOCC." MATCHCODE OBJECT zshfi_konzs.
SELECTION-SCREEN: END OF BLOCK b1.
IF so_konzs IS NOT INITIAL.
SELECT * INTO TABLE gt_lfa1 FROM sflight WHERE SEATSOCC IN so_konzs.
ENDIF.
sort gt_lfa1 by SEATSOCC ASCENDING.
loop at gt_lfa1 into lw_lfa1.
Write:/ lw_lfa1-SEATSOCC.
ENDLOOP.
There is no problem in it.