this is intentional with the new despawning sphere thing added in the beta were mobs instantly despawn if they are outside of it.
all you have to do is go to the original world spawn to collect your xp
wow i thought this was a feature because your hand is to your side when your flying and pointed out but okay.
This is a most likely a feature. I mean i takes to hands to reload a crossbow so how could you still be holding the shield
if you throw you get nether wart blocks; but if you click you get obsidian and flint and steals