Duplication glitch with donkey/mule inventory when logging off and on a server.

I was on my server coming home with my donkey, with inventory full of things. It was getting dark in game and late in real life. So I logged out on my donkey thinking I'll still be on my donkey when in log back in. When I did log back in I was still on my donkey, but there was another donkey next to me. They both had the same inventory, double the I had on me.