Excluding equal items automatically excludes unequal items?

[dirk-o]

I do a comparison (Two way) by content. Then I undisplay all items by pressing all of the buttons at the bottom, then I press the "Equal" button, all items are included, 9423 items are displayed. I press the equal button and, no files is shown, I press the unequal button and there are shown 2794 items. Now I press this button again, any item is displayed, I press the equal button, exclude all of the 9423 item, press this button again, now any item is displayed, I press the unequal button and 2794 items are displayed, but 2761 items now are excluded, 33 included. Why is it like that? I didn't exclude any unequal item by intention.