I joined my friends island then i went to a shop after that i did /is then it teleported me to a different island i did /is again i was still there and when i did /home i was taken to my friends island i could still destroy and place things its a little strange and i lost all of my items.
Do /Is Accept TWICE, and put your items in an Ender Chest or give them to the invitor so you don't lost them next time. Hope this helps, -Tac