Recently, I was playing SKYBLOCK on dancraft. I created an island, but to my horror, I messed up the cobblestone generator ;(.
I executed /is delete twice, but when I was teleported back to spawn, I still had the items I had collected from my EX-island! I tried again, and created a new island. I got everything out of the Upgraded member box, and executed /is delete. I was tp'ed back to spawn AND STILL HAD MY ITEMS! This bug can make players OP, as they can create an island, get all the stuff from the chests, then delete their island and create a new one to get double the stuff they got from their EX-island!