When you trade the sword by another one, the sword you was holding dissapear and the other one stay in your hand and in the slot but when placed in some space in the inventory you make the other desappear

Link showing:
https://drive.google.com/file/d/1BZXfMkTTZh-4b4pKoJqDBxPWCxcv3Dk_/view?usp=sharing

Thanks a lot for the report. In this case it's sound weird but it's expected that this happens.

The item damage will be calculated at each drop, because your drop-rate is set very fast you were able to time it perfectly that it get calculated with the both items the former one and the swapped one. So the mod assume that something is wrong and removed the "broken" item.

I will add a feature to lock the slot during the drop phase which should avoid such edge cases in the future.