Ok interesting.
Works fine in Single Player, but doesn't on multiplayer. Connection issue it is not as I'm connecting to the server sitting on my desk.
This is the 2387423rd server I built, so I do have some experience with MC server hosting and building, and this has me scratching my head.
I'm also OP on my own server, so it's not a restriction issue either. Capture a vid to show you what I mean.