Whenever you try putting blocks under groups within more groups, the engine will forget about these blocks.
For example, I tried organizing the map I was testing with in a group called "Developer Maps", and I put that group under another group called "Maps"
When I tried playing the project, the map was forgotten by the engine and actually won't appear under "levels".
This all occurred because I wanted to organize my assets, I think Cyberix should add a window for File management, and separate the properties panel based on what asset you're working on.