This mod seems good for letting people script robots without exposing a full language like Lua. Lua is a security liability. Scratch-like programming is also probably easier for beginners (I started programming using Scratch.) I'm impressed that the interface is implemented with formspecs.
Unfortunately, I'm not sure of the circumstances that caused it. All I know is that it had something to do with me messing around in the formspec. I haven't been able to reproduce it since. Sorry for the lack of information.