Thank you for the replies, Margaret and SAJ!
I finally see what's wrong with those pseudo-MindMaps. My own MMs are quite rigid and inflexible but with practice this should improve. I'll also check out "Mapping Inner Space".
More about my problem: I impose a time constraint on myself so that I only put down keywords. But usually I go over the time limit because I go back to my bad habits. I think it's partly the insecurity I have about my memory. I've had experiences where I reviewed my MM several days after making it and couldn't remember the meaning of certain symbols that I'd used. I've noticed though, that listening to the Memory Supercharger (I listen to it whenever I can now) does help my memory.