Shulker boxes dissapearing upon moving into inventory?

This issue affects

Moving shulker boxes into your inventory from chests.

How this differs from the expected behaviour

Swap the two items between your hotbar and the item you're hovering over.

How the issue manifests itself

When trying to load a shulker box into my full inventory with number a key, it swapped like it should with the 3 glass that was in my hotbar but disappeared a few ticks later, reverting to the 3 glass but the 3 glass was also in the chest, essentially duping the glass I guess. I immediately tried moving the other shulker boxes into the same slot the same way as the last time, only for each of the boxes to get deleted and for 3 glass to appear in the spot of where each box was swapped from. This wasn't just a visual glitch as I first assumed, as I logged back on to the extra glass still being there, with the (6)? boxes still gone. After restarting my client I tried this process again, to no yield. My guess is this has to do with the new illegal NBTS plugin? The time the items took to get snapped was the same as it was when I watched my extra NBT items get snapped. Regardless I'm extremely confused on what would have caused this or how to even perform it again due to the fact I wasn't able to replicate this. Goofy Ahh bug.