1. unpack "addon example" and quit the game (possibly with a space program savegame in control room)
2. enter the game
3. click OK when message "cannot update this addon..." appears
4. enter "Space program"
=> tech-tree freezed, blocked
5. quit to menu
6. enter addon and back to menu (without any change)
7. re-enter space program and tech-tree/control room is unblocked