I cannot mount horses/ donkeys

When I right click on my donkey (who had a chest), I get teleported into the donkey, but not on it. So I cannot ride it. I was unable to walk away, it was like I was teleported back into the donkey immediately. I exited and rejoined and the donkey was gone. I have also experienced this on a mac running Yosemite. This does not always happen. I was able to ride this donkey previously.

I have edited this world with MC Edit.

Steps to Reproduce:
1. Right click on donkey or horse
2. sometimes you will end up inside the donkey/horse, not on it.