I was playing in creative mode, on a flat world with my friends, and I had mail boxes around Y 1-3. Since that was on bedrock, here is where it begins.
         We were talking about how I hadn't filled the mail boxes in a month or two, I started filling them in and chatting. When my friend checked his box as he was standing DIRECTLY in front of it, he opened the shulker box and got his mail, and as soon as the shulker box started closing, he teleported under the bedrock and the game crashed.
         As soon as I got the game back up, I made a new world and tried it out there. It happened, but the game didn't crash and the shulker box stayed open. I was confused more than I've ever been. I tried with more, but stayed away. The shulker boxes ALSO stayed open, and the interface never showed up. The game stayed up for about 10 seconds before promptly crashing again.
        Now I'm scared of shulker boxes.