I am seriously laughing at this right now.
Honestly, I had no idea this was possible either. I know single items are supposed to be safe from robbing/stealing, so this is completely unexpected. Great to know that this game can still surprise us.
I'm sending Shoveler a new shovel, and congratulations to digslut on his unexpected windfall (you can have fun trying to figure out how to get it to a digger).
For anyone who does have a diamond shovel, I suggest equipping it to keep it safe.