Affects Version/s: Minecraft 13w36b
Fix Version/s: None
Environment:Windows 7 Home Pro x64
Core i7 920
GTX 660 Ti
java version "1.7.0_21"
Java(TM) SE Runtime Environment (build 1.7.0_21-b11)
Java HotSpot(TM) 64-Bit Server VM (build 23.21-b01, mixed mode)
While flying, I took a cow on a lead, and drag it into the air.
Then, I right clicked the cow to detach the lead. The lead disappeared, but the cow was still flying, and I was still able to move it by flying to the right or left, like it was still on the lead.
When I right clicked the cow again, I saw the lead appear for a second and then it finally disconnected the cow.
Sometimes, the bug does not appear. It'll most likely happen when you right-click the mob when it's just out-of-reach for the server, but not the client.
I also noticed the opposite can happen: the mob will be on the lead, but still be able to move (and/or fall down).
P.S.: the cow died.