Donkey/Mule Duplication glitch! Works in SMP!

I admin on a minecraft server, and while we were preparing to release our server for 1.6.1 we ran into a huge problem. If someone accesses a donkey's inventory, and then another person gets on the horse and logs out, the first person will still be able to take items from that donkey's inventory. Then, when the other plays logs back on, the donkey's inventory will reset, effectively duping the items within. Though i didn't test this with a mule, i am assuming it works the same. I DID however test this with donkeys multiple times and got the same result every time! Please fix this so servers do not have to disable horses or fear their server being ruined!