I can confirm this - I let the witches drop aprox. 30 blocks, and some of the dropped entities are ghost entities.
The entities can be moved by water streams as well as item elevators, but are still untouchable when they lay still. If another entity of the same kind is dropped on top of the untouchable entity, they stack together allowing the dropped entity to be picked up and the untouchable entity to be removed.
Replicated in SMP (1.4.5 jar)
// O
What Torabi said.
What would be of great benefit to most players would be proper key assigment, where using modifiers actually work. Right now, Mojang argues that if they enable ctrl+mouse1 as right click, they can't use the modifiers for other stuff - why not leave this up to the user? Default keys as they are, but allow for changing key binding for all inputs, not only the basic stuff. Of course, this would be considered a more advanced setup, that might be better off hidden behind an "Advanced controls" button or so, but it would allow for much more customization for the gameplay. I know that I would like to rebind certain functions to be on the same key, with modifiers, as that's how I usually set up most of my other apps where that's possible.