Your question about the units: http://www.neo-engine.de/wordpress/?page_id=47 :p
The play in editor feature is very, _very_ experimental. Currently only A-Z and the mouse work in-game. Setting the cursor position etc. is not implemented yet. I need to replace the whole SDL keyboard/mouse input system and need to integrate SDL for joystick/gamepad support. What works is the starting and stopping of the game. That was quite a chunk of work and I think that it is quite stable by now.
Btw: Did you experience and problems with the MingW version (crashes, missing dlls, sound issues etc.)? If not I will cross-compile for Windows from now on.
I will look into why the prefab plugin broke tomorrow.
Thanks for testing!