I set up a mob farm in a creative test world in 6.1.BETA26.
Set out some void spikes near a few brains in a jar and started farming mobs. After a few minutes I noticed there were no experiance orbs so I shook the brains in a jar while in survival and nothing happened. I removed the jars, farmed some more and noticed no experience orbs were appearing even when I stood far enough away to avoid picking up orbs.
I set up a mob farm in a creative test world in 6.1.BETA26. Set out some void spikes near a few brains in a jar and started farming mobs. After a few minutes I noticed there were no experiance orbs so I shook the brains in a jar while in survival and nothing happened. I removed the jars, farmed some more and noticed no experience orbs were appearing even when I stood far enough away to avoid picking up orbs.