I just recreated this. I believe it has to do with making a modification from the report screen. I started with this:
I also have the same banknote as a swap but without the mpo comment. I then edited the one with the mpo comment and changed the quantity from 3 to 4 on that screen.
After saving the screen changes to include the swap banknote as well.
So, just like you I show “0 for swap” even though there is one for swap showing. Also note that I show "3 banknotes" with comment of mpo even though I just changes the quantity to 4. If I refresh the page everything gets corrected:
This is a known bug when editing from My banknotes/coins/exonumia page and has been reported previously.