You are correct, i tried and got the same thing... and I don't think that is the way it is meant to be.
I changed your category to Issues and Errors, and modified the title to better suit the issue.
Meanwhile I found a workaround... Create another device (I just used generic) and when setting up your "shared" Button Widget, target the Generic device, set your vPin, then switch target from Generic to your Tag. It should work after that as "normal". You will get the "One of your devices is offline" error, just ignore it, or if you are done setting up tags then remove that Generic device.