about LOOP statement in PAI when working on a table control

I am working on a table control.

Here's the part of the logic.

LOOP AT gt_xxx_scr. "internal table related to the table control

    MODULE modify_data.

ENDLOOP.

MODULE modify_data is used to modify or append when the user makes some changes on TC.

The TC displayed correctly at the first place.

But after gt_xxx_scr was changed but make NO change on the TC,

the logic did go into the LOOP that makes the TC displayed incorrectly.

I think that it should not go into the loop when no change is made on the TC.