I was trying to take my horse to the nether. I couldn't push it in my portal however, because of the height difference, so I decided to use a lead.
When my horse went to the nether, I followed him. There was a strange thing about the lead: it had dropped, because the connection was broken, but I still held another one in my hand when I got there.
I know there have been several bugs in the past which made it possible to "copy" items. I think this might be another bug of that kind.
Related issues
Comments

Thank you for your report.
However, your ticket has been resolved as a duplicate.
This issue has been linked to the original bugreport: MC-15270. You can find or add further information on that report.
Please search before reporting any bugs, as it's likely that one exists already.
⚠️ Please do not mark issues as private, unless your bug report is an exploit or contains information about your username or server.