The application crashed while I was duplicating a map. I tried several things, but by removing the "patrol mode" from NPCs, I was finally able to duplicate it. If it can be useful to someone...
I tried to copy/paste elements (about 100) from one map to another, but the y axis (altitude) was lost in the process and all went underground. And it is a pain to correct each element manually. For this reason, I would also kill to have the ability to create my own custom clusters. It would greatly help!